Neapolitan Sheet Cake with Whipped Cream Cheese Frosting

!Cake

unsalted butter, softened to room temperature

granulated sugar

large eggs

all-puporse flour

cornstarch

baking powder

salt

milk (whole milk or 2% work the best)

vanilla extract

sour cream

!Chocolate Cake

cocoa powder

brewed coffee, hot

baking soda

!Strawberry Cake

all-purpose flour

strawberries, hulled and quartered

granulated sugar

cornstarch

water

drops red food coloring (optional)

!Whipped Cream Cheese Frosting

heavy whipping cream

whipped cream cheese (it must be whipped cream cheese--regular cream cheese is too dense)

powdered sugar

vanilla extract