Prepare Royal Icing

1. Using a hand mixer, beat together meringue powder and water
2. Slowly beat in sugar, until combined
3. Tint some of the icing with brown food coloring and some with green (or your favorite color for the mug)

Decorate Cookies

1. Draw an ellipse of "cocoa" with brown royal icing, fill it in, smooth icing out with a toothpick and top with mini marshmallows
2. Dust the brown icing and marshmallows with white sanding sugar. Let dry for 1-5 hours or overnight
3. Once icing has dried, use green (or whatever color you like for the mug) royal icing and trace the outline of the mug all around the cookie and under the brown "cocoa." Fill in the mug color in zigzag fashion with the royal icing and use a small spatula to smooth out the icing and give it a shake to even out the icing
4. Design the mug with candy hearts or other favorite candy as desired and let dry
5. Store in an air-tight container or sealed plastic bag for up to 1 month