2 cups (450 grams, 4 sticks) unsalted butter, at room temperature
5 cups (575 grams) confectioners sugar
2 teaspoons vanilla extract
pinch of salt
1-2 tablespoons heavy cream
Purple gel paste food coloring
Directions
With an electric mixer, beat the butter on medium speed until it becomes pale and creamy (2-3 minutes).
Add the powdered sugar and salt and beat on low until combined. Turn up to medium and beat for an additional 2-3 minutes.
Add the vanilla extract and beat to combine..
Add the cream 1 tablespoon at a time until you reach the desired consistency.
Place the white layer of the cake on an 6-inch cake board. Place about 1/2 cup of the frosting on top, and spread evenly with a palette knife. Place the next layer on top of the first and repeat the process with the next 4 layers.
Place a generous scoop of frosting on the top of the cake, and spread evenly across the top of the cake. Work your way around the sides until the entire cake is covered with a thin layer of frosting.
Let the crumb coat set in the fridge for about 30 minutes.
Once the crumb coat has set, spread a thicker layer of frosting on the top and sides of the crumb coat to create a smooth finish.
Divide the leftover frosting into 3 bowls and tint each with food coloring.
Place the frosting in 3 separate piping bags fitted with star tips to decorate the top of the cake.