Place crackers in single layer on foil-covered baking sheet sprayed with cooking spray.
Bring butter and sugar to boil in medium saucepan on medium heat; cook 4 to 5 min. or until butter is completely melted and mixture is well blended, stirring frequently. Pour over crackers; immediately spread to completely cover crackers.
Bake 8 to 10 min. or until topping is hot and bubbly; cool.
Melt white chocolate as directed on package; pour over crackers. Spread to evenly cover crackers. Top with candy-coated chocolate pieces; press gently into melted chocolate with back of spoon.
Refrigerate 1 hour. Break into squares.