Bake the cakes: Cream the butter and sugar with an electric mixer until pale and fluffy.
Add the vanilla extract and eggs and beat until combined.
In a separate bowl, combine the flour, baking powder and salt.
Add this to the butter mixture in 2 additions, alternating with the buttermilk.
Divide the mixture into 4 non-stick cake pans and dye them 4 colors.
Bake at 350F for 30-40 minutes, or until fully cooked.
Cool for 10 minutes in the pan, then transfer to a wire rack and cool completely.
Place the cakes in the freezer until firm (this will make them much easier to slice!).
Make the buttercream: Cream the butter with an electric mixer until pale and fluffy.
Add the vanilla extract and beat until combined.
Add the confectioner's sugar one cup at a time, then beat for 3-5 minutes, until fluffy.
Assembly: Flatten the cakes and remove the brown sides and bottom.
Slice each cake into 4 rings.
Swap out the rings between each cake, so that each layer of cake contains one ring of each color.
Stack the layers on a cake stand, spreading some buttercream in between each layer.
Coat the entire cake in a layer of buttercream and decorate the base of the cake with candies.
Slice to reveal the checkerboard pattern inside!