Preheat oven to 325 F. and generously grease and flour 5 (9-inch cake pans), if you only have three pans or less then you will have multiple batches rotating time in the oven.
In a large bowl cream together sugar and butter. Mix in eggs until thoroughly incorporated. Mix in vanilla extract, buttermilk, and heavy cream.
Mix in half of the flour, baking powder, and salt and when the mixture is combined, mix in the rest of the flour.
Divide the batter into five bowls (about 1 cup of batter per bowl) and add food coloring to each bowl to create a vibrant red, orange, yellow, green, and blue. Pour each colored batter into the prepared pans and spread out in an even thin layer.
Bake for 10-15 minutes or until the center is set. Do not over-bake! Once they are finished baking, remove them from the oven and pan and place on a cooling rack and allow them to cool completely.
While waiting for the layers to cool begin making the cream cheese frosting by creaming together the cream cheese and butter. Next mix in the powdered sugar and vanilla until smooth.
Place the first layer down and frost, followed by the next layer and frosting, and continue this system until finished.
Place the cake in the refrigerator for 30 minutes in order for the frosting to set and sprinkle with rainbow sprinkles, slice, and Enjoy