Heat oven to 375 degrees. Line 15-½-inch x 10-½-inch x 1-inch jelly roll pan with heavy-duty foil. Generously spray foil with nonstick cooking spray.

Arrange 40 cracker squares in bottom of pan with edges touching; set aside.

Heat ½ cup butter and ½ cup brown sugar over medium heat in medium saucepan, stirring frequently, until butter melts. Increase heat to high; boil without stirring until entire surface is covered with bubbles (about 3 minutes). Remove from heat, stir in 1 tsp vanilla.

Pour mixture over crackers, spreading evenly to cover crackers.

Bake 5 minutes; remove from oven.

Sprinkle 2 cups chocolate chips evenly over crackers. Once chips have softened, use a knife or spatula to spread across the crackers.

Sprinkle with 3 Tbsps nonpareils.

Allow to sit until chocolate is set up and firm. Break or cut into pieces. Store covered in a cool, dry place.