In bowl, mix 1.5 cups graham crackers, crushed, with 1 lb. box powdered sugar. Add 1.5 cups extra chunky peanut butter and add 2 sticks melted butter. Mix well. Pat into a 9 x 13 buttered pan. Melt dozen oz bag chocolate chips -spread on top. Put in fridge for 10-15 mins, then cut into small squares. Return to fridge until firm.