Preheat oven to 400° F. Line baking sheets with parchment paper and set aside.
In a bowl, whisk together the flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream together softened butter and confectioners' sugar. Add the egg and vanilla, and beat until thoroughly incorporated. Scrape down sides as necessary.
With mixer on low, slowly add flour mixture to the bowl. The dough is ready when most of it sticks to the paddle. When touched it, it has a little give, but does not stick to fingers.
Flour the work surface and roll dough to about 1/4 inch thick, using flour for dusting as necessary. Then, cut large circle cookies and place on one prepared baking sheet. Bake for 7 to 8 minutes, rotating halfway through.
Gather up scraps and reroll dough. Cut small circles and shape into ovals if desired. Place on second baking sheet and bake 5 minutes, or until the edges start to turn golden.
Royal Icing
For the icing, add confectioners' sugar, meringue powder and water to a stand mixer with a paddle attachment. Mix for 5 minutes until soft and glossy, until a corn syrup consistency is reached. Set aside 1/2 cup icing and add one drop red food coloring and stir to create a pink icing.
Place the white icing and pink icing in separate piping bags with number 2 tip for the pink and a number 7 for the white. Cover the bowl of any remaining icing with a damp towel. Once the cookies are dry to the touch attach the decorated feet and marshmallow tails with a small dab of icing.
Notes
Meringue powder can be found at your local chef store or craft store. You can also find it online.Pro Tip: Try making the cookies a day in advance and frosting the following day. They are less likely to leach oil back into your icing if they have time to “dry out” while still staying soft.Store in an airtight container at room temperature for up to a week.Freeze dough for up to 3 months. Wrap in plastic wrap and store in the freezer. Defrost in the refrigerator before bringing to room temperature and baking.