Grease a 13x9-inch baking pan.
In a large mixing bowl, beat 1 1/4 cups peanut butter and the butter until creamy.
Gradually beat in 1 cup powdered sugar.
With hands or wooden spoon, mix in remaining powdered sugar, the graham cracker crumbs, and 1/2 cup mini chocolate chips.
Pressed evenly into prepared pan.
Melt remaining peanut butter and remaining mini chocolate chips in a heavy-bottomed saucepan over LOW heat, stirring constantly.
Spread over graham cracker layer. Refrigerate for at least 1 hour before slicing.