Preheat oven to 350 degrees F. Prepare muffin tins with liners or spray (makes 24).
Using a stand mixer with paddle attachment, cream together butter, baking powder, sugar, salt, vanilla bean seeds and vanilla bean paste until light and fluffy, about 5 minutes. Be sure to stop halfway and scrape down the sides of the bowl.
With the mixer on the lowers speed, carefully add in egg whites, one at a time, beating well after each addition (scraping down sides as necessary).
With the mixer still on low, add in 1/3 of the flour into the creamed mixture, then half the milk, another third of the flour, the remaining milk, and then the remaining flour (scraping down sides as necessary).
Gently fold in the Rice Krispie Cereal.
Using a 1/4 cup ice cream scoop or measuring spoon, fill muffin tin.
Bake for 16-22 minutes, or just until cupcakes start to brown and the center springs back when touched. You can also insert a toothpick into the center of the cupcake, and if removed mostly clean, cupcakes are done. Make sure not to brown cupcakes as they are better when slightly less done.
Remove cupcakes from oven and cool in pan for up to five minutes, then invert onto wire rack.
Cool completely before frosting.
For the Frosting:
Using a stand mixer with a paddle attachment, cream butter in a mixing bowl until butter is soft and fluffy.
Gradually beat in powdered sugar, about 1/2 cup at a time.
Beat in the vanilla bean paste.
Gently fold in the marshmallow cream until it is thoroughly incorporated into the frosting.
Place into a piping bag (or ziplock bag with a corner snipped off), and pipe frosting onto cooled cupcakes.
