PREHEAT broiler to medium heat and adjust rack to 6 inches from heat source. (Or preheat toaster oven.) Place a piece of foil on a baking sheet.
PLACE 2 graham cracker squares in a small plastic bag. Crush with fingers or rolling pin to make very fine crumbs. Break remaining graham crackers into bite-size pieces and divide between 4 serving dishes.
DIP a sharp knife in water and cut marshmallows in half. Place graham cracker crumbs in a small dish. Press cut side of marshmallows into crumbs. Place marshmallows crumb-side-down on prepared baking sheet.
SCOOP ½ cup ice cream into each serving dish. Broil marshmallows for about 45 seconds or until golden brown. (Watch carefully to prevent burning or flaming!). Immediately lift marshmallows from pan with a thin spatula and place 3 in each dish. Sprinkle with nuts and remaining graham cracker crumbs.