This red, white and blue rosette cake is a simple vanilla cake made with creamy buttercream. The cake layers are individually colored and flavored for a perfect 4th of July surprise.
Preheat oven to 350 °F. Spray three 6-inch round cake pans or two 8-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.
In a medium-size bowl, whisk and stir together the all-purpose flour, cornstarch, baking powder and salt. Set aside.
In the stand mixer bowl fitted with a paddle attachment, beat the butter, oil, and sugar on medium-high for 5 minutes.
Add the eggs, one at a time to the stand mixer bowl and beat on medium until well incorporated.
Turn the mixer on low and add the flour mixture to the butter mixture until fully incorporated.
Add buttermilk and vanilla extract. Mix on low for 10 seconds. Scrape down the sides of the bowl. Do NOT overmix the cake batter.
Evenly divide the cake batter into 3 bowls. In one bowl add the strawberry emulsion, a drop of fuchsia food color and red food color, use a rubber spatula to quickly mix together. In another bowl add the blueberry emulsion, a drop of fuchsia food color and blue food color, use a rubber spatula to quickly mix together. Be careful to overmix or else cake will become dense. Leave the last bowl white.
Evenly distribute the cake batter among the three cake pans and bake for about 35-40 minutes or until toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.
Remove cakes from oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely. Wrap cakes in plastic wrap and place in the freezer to chill for 30 minutes.
In the stand mixer bowl fitted with the paddle attachment, beat the butter until light and fluffy, about 5 minutes.
Turn the mixer to low and gradually add the powdered sugar, followed by the heavy cream, salt and vanilla extract. Mix until incorporated completely. Scrape down sides of bowl.
Turn the mixer to medium-high and beat the frosting for about 5 minutes until light and fluffy.
Turn the mixer on low and mix for 2 minutes to push out any air bubbles.
Fill 2/3 of a piping bag fitted with a closed star piping tip and white buttercream. Set aside for stacking.
Divide the remaining buttercream into 3 bowls. In one bowl, add strawberry emulsion, followed by with a drop of fuchsia food color to build a base color then add a drop of super red food color. In the second bowl, add blueberry emulsion, followed by with a drop of fuchsia food color to build a base color then add a drop of royal blue food color.
Prepare a piping bag fitted with a closed star piping tip and red buttercream. Then repeat with the blue buttercream.
Remove the cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.
Add a small amount of buttercream onto the center of the cake board.
Layer the chilled blue cake, cut side up onto the cake board. Pipe 1/2 cup of white buttercream on top and smooth out with an offset spatula.
Place the white cake layer cut side down over the top. Pipe ½ cup of white buttercream on top and smooth out with an offset spatula. Place the red cake layer cut side down over the top.
Crumb coat and freeze for 20 minutes.
Starting with the red buttercream, pipe rosettes along the bottom of the cake. Then pipe a row of white buttercream. Repeat until the sides are covered with red and white buttercream.
Then pipe rosettes with the blue buttercream on top of the cake.