In PEOPLE’s Summer Grilling issue, on newsstands now, the author of A New Way to Bake shares a show-stopping dessert that will provide some pomp and circumstance when you cut into it in front of your guests. “I love the surprise of patriotic colors on the inside of the cake instead of the outside,” Stewart says.
The gorgeous two-layer confection uses a classic white cake recipe, buttery vanilla frosting and the easiest, all-natural red and blue fillings ever. Get the full recipe below—and if you’re looking for a cake stand to serve it on, Martha’s got you covered.
For more exclusive July 4th recipes, pick up PEOPLE’s Summer Grilling issue, on newsstands now.
Martha Stewart’s Surprise-Inside Flag Cake
3 cups unbleached all-purpose flour
1 tbsp. baking powder
1 tsp. baking soda
½ 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 ½ tsp. pure vanilla extract
1 ¼ cups whole buttermilk
2 ¼ cups unsalted butter, at room temperature
6 ¾ cups powdered sugar
1 tbsp. plus 1½ tsp. whole milk
1 tsp. pure vanilla extract
1 cup very thinly sliced strawberries
¼ cup strawberry jam
1 cup small fresh blueberries
6 tbsp. blueberry jam
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.
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.
(serving size: 1 slice)
Active time: 30 minutes
Total time: 2 hours, 15 minutes