For the cupcakes: Place a rack in the center of the oven and preheat the oven to 350 degrees. Line a cupcake tray with 12 paper liners, set aside. In a medium bowl, sift together the cake flour, baking powder, and salt. Set aside.
In the bowl of an electric mixer, cream the butter and the sugar. Add the eggs one at a time, waiting until the egg is completely mixed before adding the next. Add the vanilla, let mix completely. Remove the bowl from the mixer and manually stir in 1/3 of the cake flour mixture. Then add 1/2 the buttermilk. Continue to alternate until all the ingredients are mixed. Fold the rainbow jimmies into the batter. Do NOT overmix. Distribute batter evenly into each paper liner. I used a 1/4 cup measuring cup (it fills liners 3/4 full). Bake cupcakes for 13 - 16 minutes. Check at 12 minutes. Insert a toothpick to check, it should have crumbs but no liquid batter on it. Let cool on baking tray for 5 minutes. Move to a wire rack to cool completely.

To make the vanilla meringue buttercream: In the bowl of an electric mixer at medium-high speed, beat the butter until creamy. Turn the mixer speed down to low and add the confectioners' sugar, meringue powder, vanilla extract, and salt. When the ingredients are mixed, add the half and half and beat until the frosting turns light and creamy. If frosting is too thick, add 1 additional teaspoon of half and half. If frosting is too thin, add 2 tablespoons of confectioners' sugar. I used this tip to pipe the frosting. Decorate with sprinkles.