Flag Cake (From Scratch)

INGREDIENTS

• :
• 3 cups all-purpose flour
• ⅓ cup cornstarch
• 1 teaspoon baking soda
• 1 teaspoon kosher salt
• 1 cup + 2 tablespoons unsalted butter, at room temperature
• 3 cups granulated sugar
• 6 extra-large eggs, at room temperature
• 1 cup sour cream, at room temperature
• 1½ teaspoons vanilla extract
• 2 cups unsalted butter, at room temperature
• 24 ounces cream cheese, at room temperature
• 4 cups powdered sugar
• 24 ounces raspberries
• 16 ounces blueberries