Toss together cheeses and cornstarch in a medium bowl. Add half of bacon, onion, and remaining ingredients; stir well to blend. Spoon mixture into a lightly greased 3-qt. slow cooker. Sprinkle with remaining half of bacon.

Cover and cook on Low 2 to 3 hours or until melted and bubbly. Serve warm with crackers.

Note: We tested with Cracker Barrel Sharp and Extra Sharp Cheddar cheeses.