Preheat oven to 350. Combine the melted butter, sugar and graham cracker crumbs. Press half the mixture into the bottom of a buttered 9x13 glass baking dish. Melt the marshmallows and remaining 2 tbsp butter in 30 second intervals in the microwave stirring after each interval. When the marshmallows are melted mix in the vanilla. Spread over the crust in the dish. Sprinkle the morsels over the marshmallow. Crumble the remaining graham cracker mixture over top and firmly press with your hands. Bake for 10 minutes. Allow to cool completely, then place in fridge to harden before cutting and serving.