Preheat oven to 350°F & butter an 8 x 8-inch pan. Line with parchment paper and let ends overlap. Butter parchment.
In a medium bowl, mix together flour, oats, graham cracker crumbs, baking powder, and salt.
In a bowl of an electric mixer, beat butter and sugar. Add in egg; stir well, then mix in flour mixture until combined
Spread into prepared pan, smooth top evenly and bake until done, about 18-20 minutes. Let cool.
Once cooled, cover the cookies entirely with milk chocolate bars. Top with ghost-shaped marshmallows, making sure to place the ghosts face down, as their faces will melt under the broiler.
Move top oven rack to the next to highest position (be careful: being too close to the flame can cause parchment to burn). Set oven to a low Broil. Place bars in oven for 1-2 minutes until chocolate begins to melt and marshmallows are golden. Let cool, then use food coloring pen to add eyes and mouths to ghosts. Get them out of pan by using the excess parchment paper. Cut into bars. Serve warm or at room temperature and enjoy with a chilled glass of Stella Rosa Platinum French Vanilla!