Preheat oven to 350 degrees.

Finely crush graham crackers in the bowl of a food processor. In a separate bowl with an electric hand mixer, cream together the butter, sugar and salt until light and fluffy (beat on medium for 1-2 minutes). Add egg and vanilla and beat for 1 minute more. Fold in the flour and graham cracker crumbs with a spatula until well-blended. Reserve about 1 cup of the mixture, and press the rest of the crust into the bottom of a well-greased 9x13 glass Pyrex dish.

Break the Reese's bars into individual rectangles and place evenly over bottom of crust. Spread marshmallows evenly over top of Reese's bars. Crumble the reserved crust mixture on top of marshmallows. Bake on middle rack for 20-25 minutes, or until marshmallows are lightly toasted and puffed.

Allow to cool completely in pan before slicing into bars to serve.