Birthday Cake

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

For the chocolate layer: Whisk together flour, cocoa, baking soda, baking powder, and salt in a bowl. In another bowl, combine sugar, oil, eggs, buttermilk, and vanilla. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Stir in boiling water until batter is smooth. Pour batter into one prepared pan.

For the rainbow vanilla layers: Whisk together flour, baking powder, and salt in a bowl. In another bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla. Gradually add the dry ingredients to the wet ingredients, alternating with milk, mixing until just combined. Divide batter into four bowls, and tint each with a different food coloring.

Pour the colored batters into the remaining two prepared pans, dividing evenly. You may need to bake in batches depending on your oven capacity.

Bake chocolate layer for 30-35 minutes, and the rainbow vanilla layers for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool in pans for 10 minutes before inverting onto a wire rack to cool completely.

For the white icing: Beat butter until smooth and creamy. Gradually add powdered sugar, beating until light and fluffy. Add milk and vanilla extract, and beat until smooth.

To assemble: Place one rainbow vanilla layer on a serving plate. Spread with white icing. Top with the chocolate layer, spread with icing. Place the final rainbow vanilla layer on top, and frost the entire cake with the remaining icing.

Decorate with large candles and the '10' candle.