Preheat the oven to 350°F. Grease and flour three 9-inch round cake pans.

In a large mixing bowl combine the flour, baking powder and salt. Whisk together. Set aside.

In the bowl of an electric mixer fitted with the paddle attachment, beat the sugar and butter together until creamy. Add egg whites, one at a time, beating well after each addition. Add the extracts and mix again.

Add 1/3 of the flour mixture to the creamed mixture. Add in half of the sour cream; mix well. Pour in another 1/3 of the flour; mix until just combined. Add the remaining sour cream and milk. Mix to combine. Finally add the final 1/3 of the flour mixture. Beat until just combined. Scrape down the bowl and mix again briefly to make sure no pockets of flour remain.

Divide the cake batter into two big bowls. Tint one of the bowls with the red food color. Add a little at a time while mixing until a vibrant red hue is achieved.

Divide the remaining white batter into two bowls. Tint one bowl with the blue food color. Add a little at a time until a deep vibrant blue is achieved. Leave the remaining bowl untinted.

Pour each batter into a separate prepared baking pan. There will be more batter in the red pan than in the blue and white batter pans.

Bake the blue and white batter pans for 20-25 minutes, or until a toothpick tester comes out clean. Bake the red batter pan for 30-35 minutes, or until a toothpick tester inserted near the center comes out clean.

Let the cakes cool in the pans 10 minutes, and then turn them out onto wire racks to cool completely.

Cut the white cake layer in half horizontally using a serrated knife or cake leveler. Cut a 5-inch round from the center of the cake. Keep the 5” middle piece and whole white layer for cake assembly. Save the outer ring for cake scraps.

Combine the butter and confectioners’ sugar in the bowl of a stand mixer fitted with the whip attachment. Beat on low speed until crumbly.

Add the milk or cream to thin. Beat in the extracts.

Beat on high speed until light and fluffy. If mixture is dry add more milk or cream a little at a time until whip-able. Beat until the frosting lightens in color to opaque white, about 5 minutes.

Transfer one cup of the buttercream to a piping bag fitted with a large closed star decorator piping tip. Transfer 1/2 cup of buttercream to a piping bag fitted with a small star decorator piping tip. Set aside.

Place a 9” red cake layer on a cake board or serving plate. Top with 1/2 cup of buttercream and spread evenly. Top with a 9” white cake layer. Spread on 1/2 cup of buttercream. Next, add a 9” red layer, again frosting evenly with 1/2 cup buttercream.

Top with the 9” blue cake ring. Frost the inside of the ring with buttercream. Layer in the 5” white cake layer; cover with buttercream. Finally, layer in the 5” red cake round with the cut-side down.

Crumb coat the entire cake with a thin layer of buttercream. Save leftover buttercream for cake pop making (see notes). Refrigerate the cake until the frosting firms, about 15 minutes.

Apply a final even coat of buttercream all over the cake. Smooth evenly with a cake smoother or bench scraper. Refrigerate until firm, about 15 minutes. Then, pipe swirls of buttercream around the top edge of the cake with the reserved bag of frosting. Immediately cover with nonpareils.

Pipe a shell border around the bottom edge of the cake and immediately cover with the nonpareils.

Refrigerate the cake to firm the frosting, another 15-20 minutes. Bring the cake to room temperature before serving. Or, cut the cake while still chilled for very neat slices, but bring to room temperature before enjoying.