Preheat oven to 350 degrees F.

Line one 18” x 13” sheet cake pan with parchment paper (leave parchment paper slighter higher than the sides of the pan so it’s easier to lift the cake out after). Spray lightly with non-stick cooking spray then set aside.

In a medium bowl, whisk together flour, baking powder, baking soda and salt. Set aside.

In a separate large bowl, beat (on high speed) together butter and granulated sugar until well combined and creamy (about two minutes). Use spatula to scrape down sides of bowl.

Add eggs and vanilla into the butter mixture and beat on high until light and fluffy (about 1 minute).

Beat buttermilk into the wet mixture just until combined (about 30 seconds). The mixture may look a bit curdled but it’s okay – it will all come together nicely in the end.

Beat dry ingredients into the wet ingredients just until combined (using a spatula to scrape down sides and bottom of bowl). Do not overmix or your cake will bake up to a gummy-type texture.

Separate the cake batter equally into 6 small bowls. This works out to be about 215 grams of cake batter per bowl.

Color one bowl of batter red, one orange, one yellow, one green, one blue and one purple. Stir in the food coloring just until combined but try not to overmix.

Using spoons (one spoon per color of cake batter), randomly place different colors of cake batter around the prepared baking sheet. Try to do small spoons of cake batter so each cake slice will have a variety of colors in it once baked.

Bake in oven for 27 to 28 minutes or until toothpick inserted in middle comes out clean.

Remove cake from oven and let cool completely in pan before frosting.

Frosting Directions: In a large bowl, beat the confectioners’ sugar, butter, heavy cream and vanilla until light and fluffy (about 5 minutes). If the frosting seems too thick, beat in an additional tablespoon of heavy cream.

Smooth an even layer of white frosting over the top of the cake then frost on your desired style of rainbow or other cake decorating style.

To create the same style of rainbow as this cake: In separate small bowls, color about 2 tablespoons of frosting purple, 2 tablespoons blue, 3 tablespoons green, 3 tablespoons yellow, 4 tablespoons orange and 4 tablespoons red. Place the colored icings each into their own icing bags fitted with a Wilton 1A tip (large round tip).

Start with a small half circle of purple for the bottom of the rainbow. Start in the bottom half area of the cake – closer to the bottom if you want to fit writing over the rainbow or more in the middle if you want the rainbow more centered. Then blue above the purple, then green above the blue, then yellow above the green, then orange above the yellow then red at the top of the rainbow. If you want to blend these colors together more after they are piped, use an angled icing spatula to lightly smooth over the colors. Be careful not to smear all the colors together though.

Use a Wilton 1A tip to create fluffy white clouds around both sides of the bottom of the rainbow.

Color the remainder of the frosting blue then place this in an icing bag with a Wilton 21 icing tip (open star tip) and pipe a border around the top of the cake. Add sprinkles if desired.

The cake can remain at room temperature (wrapped well in food-safe plastic wrap) for up to 3 days. After 3 days, refrigerate or freeze the leftovers (wrapped tightly in food-safe plastic wrap then placed into a sealed food safe container). Bring the cake back to room temperature before serving.