Run a knife around edge of each cooled cake. Invert cakes, remove pans, and peel off parchment paper. Use a sharp knife to trim tops of cakes flat and even.
Cut both of the red cake layers and the white cake layer in half horizontally. You will have 4 thin red cake layers and 2 thin white cake layers.
Place a 4-inch round stencil on top of 1 thin red cake layer; cut out a 4-inch red cake round. Repeat, placing stencil on 1 thin white cake layer to make 1 4-inch white cake round. Center the 4-inch round stencil on the blue cake; cut out and remove center portion covered by the stencil to make a blue cake ring.
To assemble the cake, you will need 2 thin 8-inch red cake layers, 1 thin 8-inch white cake layer, 1 4-inch thin red cake circle, 1 4-inch thin white cake circle, and 1 blue 8-inch cake ring. Reserve the leftover thin red cake layer and other cake pieces for making crumbs for decorating.
To assemble cake, place 1 8-inch thin red cake layer on a cake pan and frost the top generously with white frosting. Place the thin 8-inch white cake layer on top of the red one, and frost the top. Place remaining 8-inch thin red cake layer atop the white one. Frost the red layer.
Place the blue ring cake on top of the 2nd red cake layer and carefully frost the inside of the blue cake ring. Gently fit the 4-inch white cake layer into the blue cake ring. Frost the top of the 4-inch white center. Place the 4-inch red cake layer on top of the white one. Gently press small cake circles flush with the top of the blue ring.
Frost the entire outside of the cake generously with the remaining frosting.
