• Preheat oven to 350°F. Grease and line 3 (9-inch) round cake pans with parchment paper. Use pans that are at least 1 ½ inches deep. Set aside.
• Stir together flour, salt and baking powder in a medium bowl. Set aside.
• Make batter for white and blue layers first. Place butter and sugar in a large bowl. Beat with an electric mixer on medium for 2 minutes. Turn mixer to low and gradually add egg whites. Continue beating until completely combined. With mixer on low, gradually add half the flour mixture and half of the milk. Mix until combined, then add remaining flour and milk. Add almond extract. Mix on medium low for 1 minute. Pour half of the batter into a prepared pan. Add blue food coloring to remaining batter. Stir to combine and pour into 2nd prepared pan.
• Meanwhile, prepare the red velvet cake mix according to package instructions. Pour all of the batter into the 3rd prepared pan.
• Bake all 3 layers for 40-45 minutes or until a toothpick inserted into middle of cake comes out clean. If possible, bake all 3 layers on the middle rack of oven.
• Let cakes cool completely. If time, cover and refrigerate cake layers for 2 hours (they're easier to work with when chilled but you can skip this step if you don't have time).
• Cut the red velvet cake (horizontally) into 3 layers. It's ok if the top layer has a dome shape (reserve this for the top layer of cake). Then cut the white cake (horizontally) to create 2 layers. Using a 4-inch round bowl, trace a circle with a knife in the middle of the blue layer. Remove the circle. Now cut the same size circle out of one of the white layers and cut the same size circle from the top (dome shape) red velvet layer. Set aside.

For buttercream:

• Place butter and shortening in a large bowl. With an electric mixer, beat on medium high for 2 minutes. Turn to low and gradually add half the sugar and half of the milk. Keep mixing until combined, then add remaining sugar and milk. Add vanilla. Once all is combined, turn mixer up to medium high and beat for 2 minutes. Add a few more tablespoons of milk if it's too thick.

How to assemble the American Flag Surprise Cake:

• Step 1 - place one red layer on a cake plate. Spread with frosting.
• Step 2 - place one white layer on top or red layer. Spread with frosting.
• Step 3 - place red layer on top of white layer. Spread with frosting.
• Step 4 - place blue layer (with the hole in the middle) on top of red layer.
• Step 5 - place a small white circle inside blue layer. Spread with frosting, then add the small red circle on top.

Frosting the cake:

• Frost the entire cake with a thin layer of frosting called a crumb coat, then frost the cake with the remaining frosting. Add toothpick flags on top for decoration, if desired. Store covered at room temperature for up to 3 days or in the refrigerator for up to a week.