Lemon Cake with Almost Homemade Buttercream

The buttermilk in this luscious lemon cake produces a moist yet fluffy crumb, and marshmallow cream gives the super simple icing a silky texture and sheen.

Ingredients

For Cake

• 1 c. ( 2 sticks) unsalted butter, at room temperature, plus more for cake pans
• 3 c. cake flour, plus more for cake pans
• 1 1/2 tsp. baking powder
• 1 tsp. kosher salt
• 1/2 tsp. baking soda
• 2 1/2 c. granulated sugar
• 5 large eggs
• 1/2 tsp. pure vanilla extract
• 3/4 c. buttermilk
• 1/4 c. fresh lemon juice
• 1 (10-ounce) jar lemon curd, for filling

For Buttercream

• 1 (16-ounce) container marshmallow cream 
• 1 1/2 c. (3 sticks) unsalted butter, at room temperature
• 5 tsp. fresh lemon juice
• 1 tsp. pure vanilla extract
• 1/2 c. confectioners’ sugar
• 1/4 tsp. kosher salt
• Blue food coloring

Directions

Step 1 Make Cakes: Preheat oven to 350ºF. Butter 2 8-inch cake pans. Line with parchment then butter and flour paper.

Step 2 Sift together flour, baking powder, salt, and baking soda in a bowl. Combine buttermilk and lemon juice in a separate bowl or measuring cup. Beat butter and sugar with an electric mixer on medium speed until light and fluffy, 1 to 2 minutes. Add eggs, one at a time, beating until combined after each addition. Beat in vanilla. Reduce mixer speed to low and beat in flour mixture and buttermilk mixture alternatively, beginning and ending with flour mixture.

Step 3 Transfer batter to prepared pans, dividing evenly. Bake until golden and a toothpick inserted in the center comes out clean, 35 to 40 minutes. Cool in pans on a wire rack for 20 minutes. Turn cakes out onto the rack and cool completely.

Step 4 Make Buttercream: Beat marshmallow cream with an electric mixer on low speed. Beat in butter until smooth. Increase speed to medium-high and beat in lemon juice, vanilla , salt, and confectioners’ sugar, scraping down the sides of the bowl occasionally, until smooth and fluffy. Reserve 1 cup icing for piping, then add desired amount of food coloring.

Step 5 Assemble Cake: Trim the tops off each cake to make them level, then split cakes into 4 layers using a long serrated knife. Stack, spreading lemon curd between layers. For the topmost layer, flip the bottom of one of the cakes upside down, to create a flat surface. Crumb coat with a thin layer of icing, then place in the fridge for at least 30 minutes to chill.

Step 6 Apply Icing: Start on the side and apply a 1/4-inch-thick layer of icing, a little at a time, holding an offset spatula vertically. Finish with top layer of icing, then apply piped dots with uncolored icing, using a pastry bag.