Blueberry Crumb Cake

Springtime is my favorite season of the year, with Autumn coming in at a close second. The flowers begin to bloom, the animals creep out of their Winter resting spaces, that bite in the air calms down so going outside is peaceful once again. Sundresses come back in rotation, whimsical picnics can be taken, and delicious, juicy berries get picked. What better way to celebrate than to bake an easy, seasonal cake like this blueberry crumb cake?

Now, I’ll be honest, blueberries are not my favorite of the berries. They’re okay in a muffin, but they’re certainly no strawberry or raspberry. So trust me when I tell you, this cake is absolutely incredible. The cake is light and fluffy, the topping crunchy and flavorful, and that blueberry filling? Fragrant, moist, fresh, a little burst of Springtime in your mouth. Serve this cake at your next brunch, pot luck, or family dinner you’re looking to make just a bit more special.

FAQs and Science

Why use frozen blueberries instead of fresh? Could I substitute for fresh?

Frozen blueberries are cheaper, and will give you a more jammy texture for the filling. That’s what I tested the recipe with, so I can’t guarantee how substituting them with fresh berries will turn out in the end.

Is the lemon juice going to bring a lemon flavor to the filling?

No, there isn’t enough lemon featured for a pronounced flavor to come through. The lemon juice just adds some brightness to the filling, so it has a bit more umph!

Could I substitute low fat/fat free sour cream for the full fat version?

Fat in baking is there for both texture and flavor. If you reduce the amount of fat used, your cake will undoubtedly end up drier and more bland than if you follow the instructions. I urge you, use the full fat version.

Does it really matter if the egg is room temperature? How can I warm it up quickly?

Having the egg at room temperature helps with the emulsification of the batter. To warm it up quickly, place the egg into a small bowl and cover it with the hottest water that comes out of your tap at the beginning of making the batter. By the time you need it, the egg will be the perfect temperature!

What You’ll Need

• 8×8 inch baking dish
• Parchment paper
• Plastic wrap
• Nonstick baking spray
• 4-quart saucepan
• Large mixing bowl
• 2 small mixing bowls
• 1 small heat-safe bowl
• Rimmed baking sheet
• Whisk
• Dry measuring cups
• Liquid measuring cup
• Measuring spoons
• Heat-safe rubber spatula
• Citrus press or citrus reamer
• Fork
• Cooling rack

The Process

The Filling

To make sure it’ll have enough time to cool down, start by preparing the filling. Place the rack in the center of the oven and pre-heat it to 350F. Line the 8×8 inch baking dish with parchment paper along the bottom and up two sides of the pan, then spray the two uncovered sides with nonstick baking spray. This way, there’s no chance of the cake getting stuck in the pan.

Grab a small mixing bowl and whisk together the sugar, flour, cornstarch, and salt. Don’t worry about any clumps in the cornstarch or flour, the sugar crystals are perfectly suited to work those out during whisking. Set the dry goods aside for a few moments.

Melt the butter in a 4-quart saucepan over medium heat. When it’s mostly melted, dump the frozen blueberries into the hot pan. Pour in the lemon juice and, using a heat-safe spatula, give the berries a stir to coat. As the berries get hot and juicy, sprinkle over the flour/sugar mixture. Stir the berries constantly until the starches in the flour and cornstarch activate and thicken the filling up. It’ll take around 10-15 minutes, but it’s worth the effort.

Immediately after the filling gets thick, pour it out onto a rimmed baking sheet. Spread it out as thin as you can, to speed up the cooling process. If there’s room in the fridge, throw it in there. You need the filling to cool down completely to room temperature before pouring it over the batter.

The Topping

Streusel is such a simple and easy component to create, but truly does elevate the texture of the cake. It comes together quickly, but it’s good to have it ready to go. In a small mixing bowl, whisk together the flour, sugar, cinnamon, and salt.

Place the butter in a small heat-safe bowl and melt it in the microwave. If the microwave isn’t an option, you could of course place it in a small pot on the stove top. But I’m lazy, so if I can defer to the microwave, I’m going to. Pour the melted butter on top of the dry goods and use a fork to toss it in there, making large chunks of streusel. Cover the bowl with plastic wrap to keep the streusel fresh, until it’s needed during assembly.

The Batter

Onto the batter! Whisk together the flour, sugar, salt, baking powder, and baking soda, in a large mixing bowl. Create a large well in the center of the dry goods, using either a rubber spatula or measuring cup. This well just makes it easier for the liquid mixture to reach the bottom of the dry goods, so you’ll have an easier time hydrating the entire batter without over-mixing.

Melt the butter. Now, I just do this directly in the small mixing bowl that all of the liquids will be combined in using the microwave, to save on time and dishes. However, much like earlier with the melted butter for the streusel, you can always melt it in a small saucepan on the stove top instead. You are in charge of your own cake. 

To the melted butter in the mixing bowl, add in the egg, sour cream, milk, and vanilla extract. Whisk them together until they’re thoroughly combined.

Grab the dry goods and pour the liquid mixture directly into the well you dug out of the center, scraping the sides of the bowl with a spatula to get as much of the mixture as you can. Every little bit counts.

Take that same spatula and gently mix the two together to form one homogeneous batter. Be sure to scrape the bottom of the bowl so that all of the flour is hydrated, leaving no streaks behind.

Assemble and Bake

Bring the lined 8×8 baking dish back into the picture. Pour all of the batter you just prepared into it, scraping the sides of the bowl it was mixed in to get as much of the batter as you can. Smooth out the top, so the batter evenly distributes throughout the dish.

Pour the now cooled blueberry filling over the batter in the pan. Try to dollop it in different sections as you go, then spread it out. If you focus solely on the center, it will weigh down the middle of the cake. Use a spatula to even the blueberries over the batter.

Sprinkle all of the streusel over the top of the blueberry filling, so it’s equally dispersed. Place the cake on the center rack of the hot oven for 65-70 minutes, or until a toothpick jabbed in the center comes out clean of batter. Flip the pan halfway through baking, to get a nice even color.

Once it’s finished, let the cake cool in the pan for at least 15-20 minutes. If you try to take it out too soon, the blueberries will splooge out everywhere and you’ll have a bad time. The 15-20 minutes allows the blueberry filling time to cool down enough to set up and stay secure. Transfer the cake over to a cooling rack, so it can completely come down to room temperature.

Slice the cooled cake into a 4×4 grid to give you 16 relatively equal slices, or whatever the desired amount of portions for you is. Serve up a slice and enjoy! Store any leftover cake in an airtight container on the counter for up to two days.

Blueberry Crumb Cake

Bake Time: 350F for 65-70 minutes
Servings: 16 servings
Total Time: 2 hours 20 minutes
Prep Time: 1 hour 10 minutes

Ingredients

Filling:

• ⅔ cup granulated sugar
• 2 Tablespoons all-purpose flour
• 1 Tablespoon cornstarch
• ½ teaspoon salt
• 2 Tablespoons unsalted butter
• 12 oz frozen wild blueberries
• Juice of 1 medium lemon

Streusel:

• ⅔ cup all-purpose flour
• ½ cup granulated sugar
• ¾ teaspoon ground cinnamon
• ½ teaspoon salt
• 4 Tablespoons unsalted butter

Batter:

• 1 ⅓ cup all-purpose flour
• ½ cup granulated sugar
• ½ teaspoon salt
• ½ teaspoon baking powder
• ¼ teaspoon baking soda
• 6 Tablespoons unsalted butter
• 1 large egg, room temperature
• ½ cup full fat sour cream
• ½ cup whole milk
• 1 teaspoon vanilla extract

Directions:

For the Filling:

1. Preheat the oven to 350F, on the convection setting if possible, and make sure the rack is in the center of the oven. Line the bottom and up two sides of an 8×8 inch baking dish with parchment paper, then spray the two uncovered sides with a nonstick baking spray. Set the pan aside until the cake is ready to assemble and bake.
2. Start by preparing the filling. In a small bowl, whisk together the sugar, flour, cornstarch, and salt. Set the dry goods aside.
3. Place a 2 quart saucepan over medium heat and add in the butter. Once it’s melted, pour in the frozen blueberries. Squeeze in the lemon juice and, using a heat safe spatula or large spoon, give the blueberries a stir.
4. After a few minutes, once the berries start to get juicy, dump the dry goods into the pan. Stir the berries constantly for around 15 minutes or so, until the filling becomes thick. Immediately pour the filling onto a rimmed baking sheet, spreading it out so it can cool down.

The Streusel:

1. Whisk together the flour, sugar, cinnamon, and salt in a small mixing bowl. Set this bowl aside for a moment.
2. In a small heat-safe bowl, heat the butter in the microwave until it’s just melted. Pour it over the dry goods and mix the two together with a fork, forming large clumps of streusel. Cover the bowl with plastic wrap and set it aside until assembly time.

For the Batter:

1. In a large mixing bowl, whisk together the four, sugar, salt, baking powder, and baking soda. Using either a rubber spatula or measuring cup, carve out a well in the center of the flour mixture, as shown above. Set this bowl aside.
2. In a small heat-safe mixing bowl, heat the butter in the microwave until it melts. Add in the egg, sour cream, milk, and vanilla extract, and whisk them until they come together smoothly.
3. Pour the liquid mixture into the well you made in the dry goods bowl moments ago, scraping as much out as you can with the spatula. Use the spatula to stir the two together to form the batter, until no streaks of flour remain.

Assemble and Bake

1. Grab the lined baking dish from the beginning of the recipe and pour all of the batter into it. Scrape in as much as you can and smooth out the top using the rubber spatula.
2. Pour the blueberry filling on top of the batter and spread it out as evenly as you can. Sprinkle the streusel equally over the blueberries.
3. Bake the cake on the center rack of the hot oven for 65-70 minutes, or until a toothpick poked in the center comes out clean of any batter. Flip the pan halfway through baking.
4. Allow the cake to rest in the pan for 15-20 minutes, then transfer it over to a cooling rack to finish coming down to room temperature. Slice the cake into 16 equal portions, or the desired amount, to serve and enjoy! Store any cake that’s leftover in an airtight container for up to two days.

Tips

• The blueberry filling can be prepared up to two days ahead of time! Follow the recipe for the filling as written, then place it in an airtight container in the fridge for up to two days. Complete the rest of the recipe as written when you’re ready to bake the cake.