HEAT oven to 400°F.
PLACE crackers in single layer in foil-lined 15x10x3/4-inch pan.
COOK butter and sugar in saucepan on medium-high heat until butter is melted and mixture is well blended, stirring occasionally. Bring to boil; cook 3 min. without stirring. Spread over crackers.
BAKE 7 min. Immediately sprinkle with chopped chocolate; let stand 5 min. Spread melted chocolate over crackers. Sprinkle with nuts; cool completely. Break into pieces.