Flag Cake

INGREDIENTS

• 3 cups sugar
• 2 half-pints blueberries
• 6 extra-large eggs at room temperature
• 18 tablespoons (2 1/4 sticks) unsalted butter at room temperature
• 1/3 cup cornstarch
• 3 cups flour
• 1 pound confectioners' sugar, sifted
• 1 cup sour cream at room temperature
• 1 1/2 teaspoons pure vanilla extract
• 1 teaspoon kosher salt
• 1 teaspoon baking soda
• 3 half-pints raspberries
• 1 1/2 pounds cream cheese at room temperature
• 1 pound (4 sticks) unsalted butter at room temperature