1. Preheat oven to 350 degrees and line pans with cupcake liners.
2. Beat butter and sugar for 3 minutes, scrape bowl as needed.
3. Add egg whites one at a time on low until fully incorporated.
4. In a separate bowl, sift flour, baking powder, baking soda and salt together.
5. Alternate adding buttermilk and the dry ingredients to the butter/sugar mixture.
6. Mix in sour cream.
7. Fold in jimmies and fill liners 3/4 full.
8. Bake for 16-22 minutes, or until and inserted knife comes out clean.
9. Buttercream: Beat butter and cream cheese. Add strawberry puree, gelatin and vanilla extract. Slowly add powdered sugar until you reach your desired consistency.