Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a medium bowl, whisk together the flour and cocoa powder.

In a large mixing bowl, beat the softened butter and granulated sugar for about 3 minutes until light and fluffy.

Add eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Alternately add the flour mixture and buttermilk to the butter mixture, starting and ending with the flour. Mix gently until combined.

Add the purple food coloring and stir until the color is evenly distributed. Adjust coloring for desired vibrancy.

In a small bowl, mix the vinegar and baking soda—it will fizz. Quickly fold this mixture into the batter for extra lift.

Divide the batter evenly between the prepared pans. Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.

Let cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Beat the cream cheese and butter together in a large bowl until smooth and creamy.

Gradually add the powdered sugar, beating until fluffy. Stir in the vanilla extract.

Once cakes are cool, layer them with frosting between the layers and cover the top and sides. Smooth or swirl as desired.

Garnish with purple sugar sprinkles, edible flowers, or a light dusting of cocoa powder.