In a large mixing bowl, combine cake mix, eggs, water, and oil.

Line two regular-sized muffin pans with paper liners.

Fill muffin cups 1/2 full.

Bake at 350 degrees for 15-18 minutes, or until edges are golden brown and the tops of cupcakes spring back when pressed with a finger.

Cool in pans for about 10 minutes before removing to wire racks to cool completely.

Using a small spoon or knife, scoop a 1-inch ball out of the center of each cupcake. Discard the scooped cake balls, or repurpose (make cake balls!).

Fill each cavity evenly with Lucky Charms marshmallows.

Combine egg whites, sugar, and cream of tartar in a heat-proof bowl, ideally your mixing bowl.

Place over top of a large saucepan of simmering water, and whisk constantly for about 2 minutes, or until the sugar has dissolved and the egg whites are warm to the touch.

Immediately remove the bowl from heat, and place in your stand mixer. Start beating the egg white mixture slowly at first, but gradually increase speed to high.

Beat for 6-7 minutes, or until glossy and thick.

Add vanilla, and beat until combined.

Pipe the frosting onto the cupcakes. Enjoy!