Line large jelly-roll pan with aluminium foil; lightly coat with nonstick cooking spray. Arrange crackers on pan in single layer.

In a large microwave-safe bowl, microwave butter on high 1 minute, or until melted. Whisk in granulated sugar, brown sugar, vanilla, and vinegar until smooth. Microwave uncovered on high 6 minutes in 2-minute intervals, whisking thoroughly after each interval before returning to microwave. Microwave 1 to 2 minutes more or until dark amber (or until candy thermometer registers 320 degrees F).

Carefully remove caramel from microwave; pour over crackers in pan. Spread caramel into a thin layer using offset spatula; tap jelly-roll pan on a flat surface to evenly distribute.

Melt chocolate in a microwave-safe bowl for 1 minute. Stir. Heat in additional 30 second intervals stirring after each one until melted and smooth. Let cool 15 minutes, or until caramel hardens;