Preheat oven to 350°F. Place graham crackers into a large resealable plastic bag. Finely crush the crackers into crumbs. Combine graham cracker crumbs, powdered sugar and butter in a small bowl.
Place 1 TBSP crumb mixture in each cup of a mini muffin pan.
Press crumbs into each cup. Lightly indent the crumbs with the back of round teaspoon.
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 kitchen scissors dipped in cold water. Place one marshmallow half, cut-side down, into each cup. Return to oven 1-2 minutes or until marshmallows are just slightly softened.
Cool in pan for 15 minutes. Carefully remove cups from pan. Cool completely.
Break remaining candy bars into a small bowl and microwave on HIGH 45-55 seconds or until melted and smooth. Carefully spoon about 1-2 teaspoons of chocolate on top of each marshmallow. Let stand 40 minutes-1 hour or until set.