• Preheat the oven to 350°F/180°C. Grease 3 x 9-inch pans with shortening or butter and dust with a tablespoon of flour each. Set pans aside.
• In a large bowl, cream together the butter and sugar with an electric mixer on medium speed. Add the eggs, one at a time, and make sure each egg is fully incorporated before adding the next. Add the vanilla extract, and beat until well blended.
• In a separate medium bowl, sift and then whisk together the flour, baking powder, baking soda, and salt to make sure it’s thoroughly combined. With a wooden spoon or spatula, gradually fold in the dry ingredients to the wet ingredients, alternating adding the flour and the buttermilk, until just barely combined. Do not over-mix the batter.
• Divide the batter equally into three small or medium bowls. (It’s best to use a digital kitchen scale to make sure the weights are equal.) Add a drop of the red and blue food coloring separately to two of the bowls of batter. Leave the other one plain. Stir the batter gently until the color is well mixed. Pour each batter into each of the 3 cake tins. Bake on the middle rack of the oven for 20-25 minutes, or until a toothpick inserted in the middle comes out clean. Let the cakes cool in the tin for about ten minutes, then transfer to a cooling rack to cool the cakes completely.

To make the buttercream:

• While the cakes are cooling, cream the 2 cups of butter with an electric hand mixer on medium speed. Gradually add in the powdered sugar (about ½ cup at a time) until all of the powdered sugar has been mixed into the butter. Pour in the vanilla extract, salt, and heavy whipping cream, and blend at low speed until completely smooth. Put about a ¼ of the buttercream into a piping bag with a large round tip.
• Put a small about of buttercream on to the base of a cake stand or platter, and place the blue cake in the middle of the stand. Pipe the buttercream around the top of the blue cake, and spiral inward until the top is covered. Use a spatula to smooth out the buttercream. Continue with the white cake and then the red cake. Use a spatula to add buttercream to the sides of the cake and spread thinly. This will be your crumb coat. Place the cake in the freezer for 20 minutes (or in the refrigerator for 40 minutes).

To decorate:

• Add a fresh layer of buttercream to the sides, then decorate with additional frosting that you've colored blue or red if desired. Add some patriotic sprinkles to finish the look.