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

In a large bowl, cream together the softened butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.

Stir in the purple food coloring until desired color is achieved.

Pour the batter evenly into the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

While the cakes are cooling, prepare the buttercream frosting. In a large bowl, beat the softened butter until light and fluffy. Gradually add the powdered sugar, beating until smooth.

Add the milk and vanilla extract and beat until light and fluffy. Stir in the purple food coloring until desired color is achieved.

Once the cakes are completely cool, frost the top of one cake layer with buttercream frosting. Top with the second cake layer and frost the entire cake with the remaining buttercream frosting.

Decorate with sprinkles or other desired decorations.