1. To make the cupcakes, prepare a cupcake pan with cupcake liners and preheat the oven to 350°F (176°C).
2. Combine the flour, baking powder and salt in a medium sized bowl and set aside.
3. Add the butter, oil and sugar to a large mixer bowl and beat together until light in color and fluffy, about 2-3 minutes. Do not skimp on the creaming time.
4. Add the eggs one at a time, mixing until mostly combined after each. Add the vanilla extract with the second egg. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Add half of the dry ingredients to the batter and mix until mostly combined.
6. Slowly add the milk and mix until well combined. The batter might look a little curdled, but that’s ok.
7. Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix the batter.
8. Divide the batter between 3 bowls. Leave one as-is for the white, color the second bowl red and the third bowl blue. Gently fold the batter to combine, so you don’t over mix.
9. Add about 4 tablespoons of batter to each cupcake liner. I added a little more than 1/2 a tablespoon of each color to make one layer, then made a second layer of the same thing again.
10. Bake cupcakes for 15-20 minutes or until a toothpick inserted into the center comes out clean.
11. Remove cupcakes from the oven and place on a cooling rack to cool.
12. To make the buttercream, beat the butter in a large mixer bowl until smooth and creamy.
13. Add about half of the powdered sugar and mix until smooth and well combined.
14. Add the vanilla extract and 1 tablespoon of water or cream and mix until smooth and well combined.
15. Add the remaining powdered sugar and mix until smooth and well combined.
16. Add more water or cream until desired consistency is reached, then add salt to taste.
17. Divide the buttercream into three bowls. Leave one as-is, color the second red and the third blue.
18. To make the swirl frosting, add each color of frosting to a ziplock bag. Lay a piece of clear wrap out on the table. Trim the corner off of each ziplock bag. Pipe a thick row of each color of frosting side-by-side onto the clear wrap.
19. Fold the clear wrap over into a long log (see photos in this post for guidance). Twist one end closed and trim the other end, if needed, so that the frosting is right at the end.
20. Put the log into a piping bag with the open end of the log going into the piping tip. I used piping tip Ateco 849.
21. Pipe swirls of frosting onto the cupcakes and serve. Cupcakes are best for 2-3 days.