4th of July Cake

Name: 4th of July Cake
Prep time: 1 h
Cook time: 30 min
Total time: 1 h 30 min
Cuisine: American
Ingredients: 18 tbsp. (2 1/4 sticks) unsalted butter, at room temperature, plus more for the pan; 3 c. sugar; 6 extra-large eggs, at room temperature; 1 c. sour cream (not low-fat), at room temperature; 1 1/2 tsp. pure vanilla extract; 3 c. all-purpose flour, plus more for the pan; 1/3 c. cornstarch; 1 tsp. kosher salt (use 3/4 teaspoon regular salt if kosher salt is not available); 1 tsp. baking soda; 1 1/2 lb. (3 (8-oz.) packages) cream cheese (not low-fat), at room temperature; 1 lb. (4 sticks) unsalted butter, at room temperature; 1 lb. powdered sugar, sifted; 1 1/2 tsp. vanilla extract; 2 half-pints blueberries; 3 half-pints raspberries