Prepare three 8 inch cake pans with parchment paper circles in the bottom and grease the sides
Preheat oven to 350 degrees
In a medium size bowl, combine the flour, baking powder and salt, set aside
In a large mixer bowl, add butter, sugar oil and vanilla extract and beat together until light in color and fluffy, about 3-4 minutes
Add the eggs one at the time, mixing until mostly combined after each, scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated
Add half of the dry ingredients to the batter and mix until mostly combined
Slowly add the milk and mix until well combined. The batter will look curled, but that is ok
Add the remaining dry ingredients and mix until well combined and smooth. Do not over mix the batter
Divide the batter in three separate bowls and add the food colors to the bowls, coloring one bowl with each color, red, yellow and green
Spread the batter into the prepared cake pans and bake for 25-30 minutes or until a toothpick comes out with a few crumbs
Remove from oven to cool completely
To make frosting:
In the bowl of an electric mixer fitted with the paddle attachment, beat butter and salt on medium speed until smooth and creamy
Slowly add half of the powdered sugar and mix until smooth
Add heavy cream and vanilla extract and mix until smooth
Slowly add the remaining powdered sugar and mix until smooth, beat in more powdered sugar if frosting too thin
To Assemble the Cake:
To put the cake together, use a large serrated knife to remove the domes from the top of the cakes so that they are flat
Place the first cake on a serving plate or a cardboard cake round
Spread about 1 cup of frosting evenly on top of the cake
Add the second layer of cake and another cup of frosting
Top the cake with remaining layer and frost the outside of the cake
Sprinkle top of the cake with sprinkles and press sprinkles into sides of the cake if desired
