Beat butter & sugar.

Add egg and vanilla.

Add flour, cocoa and salt.

Once dough forms, roll out on lightly floured surfce, cut out shapes and bake at 350 for 10-13 mins.

Royal icing:

Beat ingredients in a mixer bowl on low speed until smooth, about 7 minutes.

If icing is too thick, add more water; if too thin, beat 2 to 3 minutes more.

Pipe icing onto cookies and decorate with red sugar and marshmallows.