Make the Funfetti Cupcakes:

1. Preheat oven to 350 degrees and line muffin pans with cupcake liners.
2. In bowl of stand mixer combine all dry ingredients: flour, sugar, baking powder and salt.  Beat for 2 minutes until well combined.
3. Add butter a few cubes at a time beating on low until resembles coarse sand.
4. Add egg whites and beat on medium speed until well combined.
5. Add milk and vanilla and mix on medium speed 1-2 minutes until well combined, scraping sides of bowl as necessary.
6. Fold in rainbow jimmies.
7. Fill cupcake liners 2/3 full with batter.
8. Bake for 18-20 minutes or until toothpick inserted in center comes out clean.
9. Let cupcakes cool in pans for 5 minutes, then remove to wire racks to finish cooling.
10. Once cupcakes are completely cool frost with Fluffy Vanilla Buttercream.

Make the Fluffy Vanilla Buttercream:

1. In bowl of stand mixer beat butter on medium speed for 4 minutes until light and fluffy.
2. Add confectioner’s sugar, vanilla and milk and beat on medium speed for 6 minutes, scraping sides of bowl as necessary.
3. Use an offset spatula to spread on desired amount of icing.
4. Add rainbow jimmies to a bowl and dip the edge of your iced cupcake into the sprinkles and gently twist around in a circular motion until the edges are covered.