COOK and stir bacon in large saucepan on medium heat until crisp. Remove bacon from pan with slotted spoon; drain on paper towels. Discard all but 2 Tbsp. drippings from pan.
ADD onions to reserved drippings in pan; cook 20 min. or until golden brown, stirring frequently. Add broth, pepper and thyme; stir. Simmer 15 min. Remove from heat; stir in bacon.
HEAT broiler. Ladle soup into 5 ovenproof bowls; top with remaining ingredients.
BROIL, 4 inches from heat, 2 to 3 min. or until cheeses are melted and golden brown.