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Lemon Buttermilk Cake with Blueberry Filling

Fluffy lemon buttermilk cake layers with blueberry jam filling and creamy lemon buttercream.

Course Dessert
Cuisine American
Keyword blueberry, Buttercream, Cake Decorating, Cake Recipe, Frosting, lemon
Prep Time 1 hour
Cook Time 1 hour
Cooling/Decorating Time 2 hours
Total Time 4 hours
Author Katie

Ingredients

Lemon Buttermilk Cake

  • 3 cups cake flour (or 2 ¾ cups all-purpose flour + ¼ cup cornstarch)
  • 2 teaspoons baking powder
  • 1 teaspoon salt
  • 1 cup (or 2 sticks) unsalted butter, room temperature
  • 1/2 cup vegetable oil
  • 2 cups granulated sugar
  • 6 large whole eggs
  • 2 large egg yolks
  • 2/3 cup buttermilk
  • 1/3 cup lemon juice
  • 1 teaspoon vanilla extract
  • 4 Tablespoons lemon zest

Blueberry Jam Filling

  • 1 1/2 cups blueberries, fresh or frozen
  • 1/2 cup granulated sugar
  • 2 teaspoon lemon juice
  • 1 Tablespoon cornstarch
  • 1 Tablespoon water

Lemon Gel

  • 1/2 cup lemon juice
  • 2 Tablespoons cornstarch
  • 2 Tablespoons lemon zest

Lemon Buttercream

  • 2 cups (or 4 sticks) unsalted butter, room temperature
  • 1/4 cup lemon gel recipe (as seen above)
  • 1 teaspoon salt
  • 1 teaspoon vanilla extract
  • 7 1/2 cups powdered sugar, sifted
  • 2-3 Tablespoons heavy cream

Instructions

Lemon Buttermilk Cake

  1. Preheat the oven to 325 °F. Spray three 6-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper.

  2. In a medium-size bowl, whisk and stir together the cake flour, baking powder, and salt. Set aside.

  3. In the stand mixer bowl fitted with a paddle attachment, beat the butter, sugar, and oil on medium-high for 5 minutes.

  4. Add the eggs, one at a time to the stand mixer bowl and beat on medium until well incorporated.

  5. Turn the mixer on low, add the flour mixture, followed by the buttermilk.

  6. Pour in lemon juice, vanilla, and zest. Mix on medium for another 30 seconds then scrape down the sides of the bowl.

  7. Evenly distribute the cake batter among the three cake pans and bake for about 35-45 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.

  8. Remove cakes from the oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely — wrap cakes in plastic wrap and place in the freezer to chill for at least 30 minutes.

Blueberry Jam Filling

  1. In a medium saucepan, mix the blueberries and sugar. Continue mixing with a rubber spatula over low-medium heat until the sugar has dissolved and the berries begin to boil.

  2. In a small bowl, combine the cornstarch and water. Add cornstarch mixture to the boiling berries and continue to stir with a rubber spatula.

  3. Continue cooking the mixture for 2-3 minutes until it is thickened and coats the back of a spatula. Remove from heat and add lemon juice.

  4. Pour the blueberry filling into a small bowl to cool. Press plastic wrap directly onto the surface to prevent a skin from forming. Set aside to fully cool.

Lemon Gel

  1. In a small saucepot, whisk together lemon juice and cornstarch. Place the pot over medium heat for 2-5 minutes to bring to a boil, stir with a rubber spatula constantly to prevent it from burning on the bottom.

  2. Add lemon zest to the mixture. The lemon should be opaque and thick. Once thick, remove from the heat and place into the freezer to cool quickly.

Lemon Buttercream

  1. In the stand mixer bowl fitted with the paddle attachment, beat the butter until light and fluffy, about 2 minutes.

  2. Turn the mixer to low and add the cold lemon gel, salt, and vanilla.

  3. Next, gradually add powdered sugar, followed by the heavy cream. Mix on medium-high speed for about 5 minutes, until light and fluffy. Scrape down the sides of the bowl.

  4. Place ⅔ cup buttercream into a piping bag fitted with #844 star tip.

  5. Before using, turn the mixer on low and mix for 2 minutes to push out any air bubbles or use a rubber spatula to push out the air bubbles. (You may need to repeat this step when frosting the outside of the cake).

Assemble

  1. Remove the lemon cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.

  2. Add a small amount of buttercream onto the center of the cake board.

  3. Layer a chilled lemon cake, cut side up onto the cake board. Place a thin layer of buttercream on top of the cake then pipe two rings of buttercream stacked on top of one another. Add 1/4 cup of blueberry jam inside the ring of buttercream.

  4. Place another cake layer cut side down over the top. Repeat the process for another layer—Crumb coat and freeze for 30 minutes.

  5. Next, fill a piping bag that's fitted with a #844 star tip with lemon buttercream.

  6. On the frozen cake, start from the bottom while spinning the cake, squeeze consistent pressure on the piping bag, and pipe a row around the cake. Then pipe another row directly on top of the previous row. Make sure to line up the starting point for a straight seam in the back of the cake.

  7. Repeat this process all over the sides of the cake.

  8. Then with the same piping bag and tip pipe, a rope border on top of the cake, leaving the center open.

  9. Finally, fill in the top of the cake with blueberry jam. Serve at room temperature and enjoy!

Recipe Notes

  • Read through all the ingredients and instructions so you can get a better idea of how much time and what you need to make this cake.
  • A single batch of this cake recipe makes three, 6-inch round cake layers or two 8-inch round cake layers. Double the cake recipe to make enough cake batter for three, 8-inch cake layers.
  • In this cake recipe, you need ½ cup buttermilk; if you don't have any buttermilk on hand, you can easily use ½ cup whole milk mixed with 2 teaspoon lemon juice or white vinegar to make your own. 
  • To make cake flour at home, mix 2 ¾ cups all-purpose flour and ¼ cup cornstarch. Sift or whisk together to get rid of any lumps. 
  • Be careful not to overmix this cake batter, or else the cake will come out dense. Mix until all ingredients are well incorporated.
  • You can bake the cake layers ahead of time. Wrap the cake layers in plastic wrap and freeze up to one month. 
  • You can make the lemon buttercream and blueberry jam filling a day ahead and refrigerate them overnight. Then take them out to come back to room temperature. Make sure the buttercream is at room temperature before re-whipping.