Spray or butter and flour a 8x8 inch baking pan. Alternately you can line it with parchment paper. Set aside. 

Cream the butter in a standing mixer, and add sugar. Continue to cream until light and fluffy; about 30 seconds. Add the egg. Mix until incorporated, and then add vanilla, baking powder, and salt. Give it anther good mix, and then add the flour and graham crumbs. Mix until well incorporated, then add marshmallows chocolate chunks. Stir gently until they are mixed in. 

Press into prepared pan and top with additional mini marshmallows and chocolate chunks if desired. Bake at 350° for 25-30 minutes, or until edges are golden. Middle will set completely as it cools.

If desired, prior to serving and after bars are almost completely cooled, use a kitchen torch to golden up the marshmallows even further. Serve immediately. Store in an airtight container for up to three days. Makes 12 to 16 cookie bars.