Preheat the oven to 350°F. Liberally spray three 8-inch round pans with cooking spray.
In a medium bowl, whisk together the flour, baking powder and salt. Set aside for just a minute.
In the bowl to your stand mixer, use the whisk attachment to beat the butter, oil and granulated sugar on high until smooth. This will take about 2-3 minutes.
Add the vanilla and one egg and beat until the egg is mixed in thoroughly. Add the additional eggs, one at a time, beating on high until combined before adding the next one in.
Add ⅓ of the flour mixture to the bowl. Beat on high until mixed in.
Add ½ of the buttermilk to the bowl and beat on high until combined. Continue alternating between the flour mixture and buttermilk until all the ingredients are mixed in and you have a smooth batter.
You should have 6 cups of cake batter. Transfer 2 cups of the batter to one of your prepared pans. Set aside for a moment. Divide the remaining 4 cups of batter between two bowls. Color one bowl of batter with blue food coloring and the other with red food coloring.
Transfer the blue colored batter to the second prepared pan and transfer the red batter to the third pan.
Bake all three in a preheated oven for 22-24 minutes. Move the pans around the oven at about the halfway mark. The edges of the cakes will be browned and the color in the batter will have darkened. Cool in the pan for 5-7 minutes before flipping out to a cooling rack to cool completely.
Once the cakes have cooled, we’ll begin assembly. If you have to, use a knife to level each cake so that they are even.
Use a bit of frosting to attach the blue layer onto your serving platter. This will keep the cake from moving around your dish while you are decorating. Cover the top with an even layer of frosting about a half an inch thick. Keep the frosting as even as possible.
Layer the white cake over the blue one and press lightly to adhere it to the frosting. op the white cake with a layer of frosting.
Place the red cake over the white one and press lightly.
Frost the entire outside of the cake with the remaining white icing.
Reserve a bit of frosting so you can have fun with some decoration and sprinkles.
Serve immediately when ready.