Preheat the oven to 350 degrees F (175 degrees C). Grease and flour two 8-inch or 9-inch round cake pans.

In a large bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt. Set aside.

In a separate large bowl, cream together the butter and granulated sugar until light and fluffy.

Beat in the eggs one at a time, mixing well after each addition.

In a small cup, combine the buttermilk, purple food coloring, and blueberry extract.

Alternate between adding the dry ingredients and the buttermilk mixture to the wet ingredients, beginning and ending with the dry ingredients. Blend until just combined – don't overmix!

Divide the batter between your prepared pans.

Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 15-20 minutes before inverting onto a wire rack to cool completely.

In a large bowl, beat together the cream cheese and butter until smooth and fluffy.

Add the powdered sugar, one cup at a time, until fully incorporated.

Stir in the vanilla extract.

Level the tops of the cakes if needed for a flat stacking surface.

Place one cake layer on a serving plate and spread with a layer of frosting.

Place the second cake layer on top and frost the entire cake with a generous layer of frosting.