In a medium-sized mixing bowl, cream together melted butter and sugars until light and fluffy. Add the egg, beating well. Stir in vanilla. Set aside.
Combine dry ingredients and gradually stir into the creamed mixture until just combined.
Fold in candy corn and marshmallows.
Chill the dough for a half an hour in the refrigerator.
Remove chilled dough and let sit for five minutes until slightly softened. Use a 2-inch scoop to drop cookies onto a baking sheet covered with parchment paper or a baking mat. When forming the cookies, make sure the edges are sealed, meaning no marshmallows or candy corn are sticking out at the edge. This will keep the candy corn and marshmallows from melting out.
Bake at 350°F for 10-12 minutes, until lightly browned. Remove and cool for twenty minutes.