Preheat oven to 375 degrees.
In a medium mixing bowl, whisk together flour, graham cracker crumbs, baking soda, and salt.
In a separate mixing bowl, cream together butter, peanut butter, and sugars on medium speed until light and fluffy, about five minutes. Add egg and vanilla and continue to mix until incorporated.
Turn mixer to low. If using a stand mixer, change out to the paddle attachment. Turn mixer on low and slowly add the flour. Blend just until flour is incorporated, scraping down the sides of the bowl at least once.
Scoop dough by the tablespoonful onto a prepared baking sheet, leaving at least 1-1/2 inches between the cookies. Bake for four minutes.
Remove cookies from the oven. Top each cookie with a marshmallow. Return pan to the oven and bake for an additional 4-5 minutes, or until the marshmallows are golden brown. Remove from oven and immediately top each with a chocolate piece.
Let cookies cool on the pan for 5 minutes before carefully removing to a wire rack to continue cooling. Store in remainders in an airtight container.