Ingredients:
- 2 1/2 cups (300g) all-purpose flour, plus more for dusting the pans
- 1 tablespoon baking powder
- 1/2 teaspoon baking soda
- 1/4 teaspoon salt
- 1 cup (2 sticks, 227g) unsalted butter, softened
- 1 3/4 cups (350g) granulated sugar
- 2 large eggs
- 1 teaspoon vanilla extract
- 1 1/4 cups (300ml) buttermilk
- 1 cup (2 sticks, 227g) unsalted butter, softened
- 4 cups (480g) powdered sugar, sifted
- 1/4 cup (60ml) heavy cream
- 2 teaspoons vanilla extract
- Pinch of salt
- Gel food coloring: Purple (various shades, like lavender, royal purple, and grape)
Instructions:
- Preheat oven to 350°F (175°C). Grease and flour three 6-inch round cake pans. Line the bottoms with parchment paper rounds.
- Whisk together dry ingredients. Cream butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla. Alternate adding dry ingredients and buttermilk, beginning and ending with dry ingredients.
- Divide batter evenly among prepared pans. Bake until a toothpick inserted into the center comes out clean. Let cool in pans for 10 minutes, then invert onto a wire rack to cool completely.
- Cream softened butter until smooth. Gradually add sifted powdered sugar, alternating with heavy cream, until light and fluffy. Stir in vanilla extract and salt.
- Divide buttercream into several bowls. Tint each bowl with a different shade of purple gel food coloring.
- Level the cake layers if necessary. Place one cake layer on a serving plate or cake turntable. Spread with a layer of vanilla buttercream. Repeat with remaining layers.
- Frost the entire cake with a thin layer of vanilla buttercream (crumb coat). Chill for 30 minutes to set. Then, frost the cake with a final, thicker layer of vanilla buttercream.
- Fill piping bags fitted with a large open star tip with the different shades of purple buttercream. Pipe rosettes all over the cake, starting at the bottom and working your way up. Overlap the rosettes for a full, cascading effect.
- Chill the cake for at least 30 minutes before serving.