Martha Stewart’s Surprise-Inside Flag Cake

By charlotteh371

Ingredients

• CAKE LAYERS
• 3 cups unbleached all-purpose flour
• 1 tbsp. baking powder
• 1 tsp. baking soda
• 1/2 tsp. coarse salt
• 1 cup unsalted butter, at room temperature, plus more for pans
• 2 cups granulated sugar
• 4 large eggs, at room temperature
• 1 1/2 tsp. pure vanilla extract
• 1 1/4 cups whole buttermilk
• VANILLA ICING
• 2 1/4 cups unsalted butter, at room temperature
• 6 3/4 cups powdered sugar
• 1 tbsp. plus 1 1/2 tsp. whole milk
• 1 tsp. pure vanilla extract
• FRUIT FILLING
• 1 cup very thinly sliced strawberries
• 1/4 cup strawberry jam
• 1 cup small fresh blueberries
• 6 tbsp. blueberry jam

Preparation

Step 1

Prepare the Cake Layers
1. Preheat oven to 350°F. Butter 2 (8×2-inch) round cake pans; line with parch­ment-paper rounds, and butter parchment. Whisk together flour, baking powder, baking soda and salt in a medium bowl.

2. Beat butter with an electric mixer on medium speed until softened, about 2 minutes. Add sugar, and beat until pale and fluffy, about 4 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla.



3. Reduce speed to low, and slowly add flour mixture in 2 batches, alternating with buttermilk and beginning and ending with flour mixture; beat just until incorporated.

4. Divide batter evenly between prepared pans. Bake, rotating halfway through, until cakes are golden brown and a wooden pick inserted into centers comes out clean, 30 to 35 minutes. Transfer pans to a wire rack; cool 15 minutes. Remove cakes from pans to racks, and cool completely.

Prepare the Vanilla Icing
5. Beat butter and 1 ½ cups powdered sugar with an electric mixer on medium speed until pale and fluffy. Reduce speed to medium low; gradually add remaining 5 ¼ cups powdered sugar. Increase speed to medium high. Add milk and vanilla, and beat until pale and fluffy, about 3 minutes.

Prepare the Filling
6. Combine strawberries and strawberry jam in a bowl. In another bowl, combine blueberries and blueberry jam.

Assemble Cake
7. Using a large serrated knife, trim cake tops until level; cut each cake layer in half horizontally. Fill a small pastry bag with 1⁄2 cup of the icing; cut a ¼-inch tip. Transfer 1 layer to a cake stand or platter.

8. Pipe a ring of icing around the outer edge of the cake layer; spread blueberry mixture evenly inside the icing circle. Place another cake layer on top; spread evenly with 1 cup icing. Place a third cake layer on top; pipe a ring of icing around the outer edge of the cake layer; spread strawberry mixture evenly over the layer inside the icing circle. Place remaining cake layer on top. Spread a thin layer of icing over top and sides of cake to form a crumb coat; refrigerate until firm, about 30 minutes. Using an offset spatula, spread remaining icing over top and sides of cake, smoothing sides and creating swirls on top.