Sift together flour, baking powder and salt and set aside.
Beat the butter and sugar on high until light and fluffy.
Using a fork whisk egg whites, milk and extract together in a bowl.
Alternate the dry and wet ingredients into the butter mixture beating on medium until incorporated.
Fill cupcake molds 3/4 of the way full.
Bake in a 350 degree oven for 12-15 minutes. Start with 12 minutes, check on the cupcakes and if they need more time leave them in for another few minutes. Do not over bake.
Once cooled, remove a little from the center and fill with marshmallow cream and a few Lucky Charms marshmallows!
How to Make the Buttercream Frosting
In an electric mixer, combine the room temperature butter and beat until smooth.
Add in the sugar and the vanilla and continue to beat until smooth and fluffy.
Divide the buttercream into four bowls and dye each one a different color. Pink, blue, green, yellow and purple. Use about one to two drops for each color.
In a piping bag, with the fitted tip scoop a small amount of each color next to each other, or on top of. Repeat until the bag is full. You want a rainbow effect, so you can't scoop all the color in at once, it needs to be divided throughout the bag to come out with all the colors.
Pipe the frosting onto each marshmallow filled cupcake and add a Lucky Charm to the top!