This is the perfect party cake for a July Fourth party or cookout. The frosting recipe provides the large quantity needed to fill, frost, and make the rope border for the cake. You will have a little frosting leftover. Use it to attach the firecrackers to the outside of the cake. SweeTarts Ropes candies were used for the firecrackers can be found at most US grocery stores. You could also use strawberry licorice ropes or Twizzlers.
Preheat the oven to 350F. Coat four 6-inch round cake pans with flour-based baking spray.
In a large mixing bowl, whisk together the flour, baking powder and salt.
In the bowl of an electric stand mixer, cream the butter and sugar together until fluffy. Add the eggs one at a time until combined. Add the egg white and beat again. Add yogurt and vanilla extract.
Add the flour and buttermilk alternately; begin and end with flour. Scrape down the sides of the bowl and fold together by hand until all the ingredients are well incorporated.
Divide the batter evenly into four bowls (slightly more than 2 cups per bowl). Leave one bowl untinted. Mix red food color into one of the bowls; begin with 1/2 teaspoon and increase amount until the desired vibrant red hue is achieved. Tint another bowl with the sky blue food color, and the last bowl with the royal blue food color. Mix well until no streaks of white remain. Transfer batters to the prepared pans and bake for 40 minutes, or until cakes are completely set and a toothpick tester comes out clean.
Remove cakes to a wire rack to cool completely. Trim domes from the tops of the cakes with a serrated knife to level.
Buttercream
In the bowl of an electric mixer with the whip attachment, beat butter until creamy. Add half of the confectioners’ sugar. Beat until combined. Add the remaining confectioners’ sugar and beat on low speed. Add milk or cream a little at a time until mixture whips and is of spreading consistency. Add the vanilla extract and beat again. Beat on high speed until light and fluffy.
Remove about 2/3 cup of white frosting to a piping bag.
Place 1/3 cup in each of three bowls. Cover remaining frosting in the bowl with a damp towel to prevent drying.
Tint one bowl with red food color, one with sky blue, and one with royal blue. Transfer each to their own piping bags. Lay a piece of plastic wrap on a work surface and pipe a line of royal blue frosting 8-inches long. Pipe a light blue line alongside it, followed by a white line, and red line, and another white line of frosting, all touching each other. Roll the frostings up together in the plastic and twist the ends. Snip one end. Place the snipped end into a piping bag fitted with Ateco #824 open star tip. Set aside.
Tint the remaining frosting with a small amount of sky blue food color and beat until a light blue color is achieved.
Assembly
Place the royal blue cake layer on a serving plate. Cover with a thin layer of buttercream. Stack the light blue layer on top; cover with a thin layer of buttercream. Continue with the with the white layer and frosting. Top with the red cake layer. Crumb coat the outside of the cake and refrigerate until set, 15 minutes. Coat the cake with a final layer of sky-blue buttercream. Use a bench scraper or cake smoother to smooth the edges of the cake. Refrigerate until firm, 15 minutes.
Use the reserved bag of multicolor frosting to pipe a fat rope of buttercream along the top edge of the cake. Immediately add white confetti, white nonpareils, and gold dragees while the buttercream is still tacky. Reserve any leftover frosting.
Firecrackers
Cut SweeTart Ropes int 1 1/2 to 2-inch pieces. Snip the licorice lace into small pieces using a kitchen-dedicated pair of scissors. Use a toothpick to make holes in the cream centers of the rope pieces. Insert a piece of licorice lace into the holes to make a firecracker ‘wick’.
Using a toothpick place small dots of buttercream on the backs of each firecracker and attach to the outside of the cake. Repeat with star confetti sprinkles. Use a pair of kitchen dedicated tweezers to apply them to the outside of the cake. Refrigerate cake. Bring to room temperature before serving.
Notes
The cake's texture improves after a night in the refrigerator. Consider making the layers a day ahead. After they cool, wrap in plastic and store in the refrigerator until ready to use. If you can't find SweeTarts cherry ropes, try using red licorice ropes or Twizzlers.