Combine the milk and white vinegar in a small glass and set in the fridge for 15 minutes. This will make homemade buttermilk!

Cream the butter and brown sugar with an electric mixer until pale and fluffy. Add the eggs one at a time. Combine the flour, baking powder and salt in a bowl. Add to the egg mixture in 3 additions, alternating with buttermilk.

Pour into a jelly roll pan lined with parchment paper and bake at 325F for 30 minutes. Cool in the pan for 10 minutes, then transfer to a wire rack and cool completely.

Place the red and blue buttercream into piping bags fitted with #80 piping tips. Place the tan buttercream in a piping bag fitted with a 2B basketweave piping tip.

Using a large and small plate, cut out 1 large circle of cake and 3-4 small circles of cake. Place the large circle of cake onto the serving platter of your choice. Set aside. Stack the small circles on cake on top of each other and carve into the top of the hat. Spread a thin layer of buttercream onto the center of the large circle of cake and place the top of the hat on top. Pipe a basketweave pattern using the tan buttercream. Pipe flowers using the red and blue buttercream. Enjoy!