Beat egg and sugar until fluffy. Add vanilla, shortening and melted chocolate. Blend well. Combine all dry ingredients into small bowl. Add dry ingredients alternately with milk to chocolate mixture. If using, add nuts. Drop by tablespoons onto greased cookie sheet.
Bake at 350 degrees for about 8-10 minutes. When the cookies are almost done cooking, remove from oven and place 1/2 of a large marshmallow on top of each cookie. Return to oven for about 1 minute or just until marshmallow puffs. Remove from oven, flatten marshmallow with the back of a wooden spoon or spatula. Cool completely. Frost with chocolate frosting.
for frosting:
Beat softened butter in bowl. Add vanilla. Slowly beat in cocoa, powdered sugar, milk or half and half. If needed, add more milk, a little at a time.