Place graham crackers into a large resealable plastic bag. Finely crush into crumbs. Combine graham cracker crumbs, powdered sugar, and butter in a small bowl.
Place 1 tablespoon of crumb mixture in each cup of a mini muffin pan. Press crumbs to form shallow cups. Bake 4-5 minutes or until edges are bubbling. Meanwhile, break two of the candy bars into rectangles. Remove pan from oven; place one rectangle into each cup.
Cut marshmallows in half crosswise using shears dipped in cold water. Place one marshmallow half, cut-side down, into each cup. Return to oven 1-2 minutes or until marshmallows are slightly softened. Remove pans from oven to cooling rack; cool 15 minutes. Carefully remove cups from pan. Cool completely.
Break remaining candy bars and place in small microwavable bowl. Microwave on high 1 to 1 1/2 minutes or until melted and smooth, stirring every 20 seconds. Dip the top of each marshmallow in melted chocolate. Turn top-side up and let stand 40 to 60 minutes or until set.