HEAT oven to 400°F.
COOK butter and sugar in saucepan on medium-high heat 5 min. or until butter is melted and mixture is well blended, stirring occasionally. Bring to boil; cook 3 min. without stirring. Meanwhile, arrange crackers in single layer in foil-lined 17x11-1/2x3/4-inch pan.
SPREAD sugar mixture onto crackers.
BAKE 7 min. Immediately sprinkle with chocolate. Let stand 5 min. or until chocolate is melted; spread to cover crackers. Top with nuts; cool completely. Break into pieces.
serving size = 1 "bar" (40 g)