Place crackers in single layer on bottom of foil-lined 15x10x1-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. (Do not stir.)
Pour over crackers; spread to evenly cover crackers.
Bake 5 to 7 min. or until topping is golden brown. Immediately sprinkle with chocolate; let stand 5 min. or until softened.
Spread over crackers; top with nuts. Cool completely before breaking into pieces.
