Ingredients
- 18 tablespoons unsalted butter, at room temperature
- 3 cups sugar
- 6 extra-large eggs, at room temperature
- 1 cup sour cream, at room temperature
- 1 1/2 teaspoons pure vanilla extract
- 3 cups flour
- 1/3 cup cornstarch
- 1 teaspoon kosher salt
- 1 teaspoon baking soda
- 1 lb unsalted butter, at room temperature
- 1 1/2 lbs cream cheese, at room temperature
- 1 lb confectioners' sugar, sifted
- 1 1/2 teaspoons pure vanilla extract
- 1 pint blueberries
- 1 1/2 pints raspberries
For the icing
To assemble
Directions
- Heat the oven to 350 degrees F.
- Butter and flour an 18 by 13 by 1 1/2-inch sheet pan.
- Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment on high speed, until light and fluffy.
- On medium speed, add the eggs, 2 at a time, then add the sour cream and vanilla.
- Scrape down the sides and stir until smooth.
- Sift together the flour, cornstarch, salt, and baking soda in a bowl.
- With the mixer on low speed, add the flour mixture to the butter mixture until just combined.
- Pour into the prepared pan.
- Smooth the top with a spatula.
- Bake in the center of the oven for 20 to 30 minutes, until a toothpick comes out clean.
- Cool to room temperature.
- For the icing, combine the butter, cream cheese, sugar, and vanilla in the bowl of an electric mixer fitted with the paddle attachment, mixing just until smooth.
- Spread three-fourths of the icing on the top of the cooled sheet cake.
- Outline the flag on the top of the cake with a toothpick.
- Fill the upper left corner with blueberries. Place 2 rows of raspberries across the top of the cake like a red stripe.
- Put the remaining icing in a pastry bag fitted with a star tip and pipe two rows of white stripes below the raspberries. Alternate rows of raspberries and icing until the flag is completed.
- Pipe stars on top of the blueberries.
- Ina serves this cake right in the pan.
- If you want to turn it out onto a board before frosting, use parchment paper when you grease and flour the pan.