French Onion-Beef Sliders

MELT 2 Tbsp. butter in large nonstick skillet on medium heat. Add onions; cook 15 min., stirring frequently. Add bouillon cube and water; cook and stir until bouillon cube is dissolved. Simmer on medium-low heat 15 min. or until onions are tender and golden brown, stirring occasionally.

STIR in 1 tsp. Worcestershire sauce and 1/2 tsp. thyme. Add meat; mix lightly. Cook and stir 2 min. or until heated through. Remove from heat.

HEAT oven to 400°F. Transfer rolls from package to cutting board, taking care not to separate rolls. Use serrated knife to carefully cut block of rolls horizontally in half. Place bottom half of rolls in 13x9-inch baking dish; top with layers of cheese, meat and onions.

MELT remaining butter; mix with mustard, and remaining Worcestershire sauce and thyme until blended. Brush half the butter mixture onto cut sides of top halves of rolls; place, buttered sides down, over topped roll halves in baking dish. Brush with remaining butter mixture.

BAKE 5 to 7 min. or until cheese is melted and all ingredients are heated through. Cut into individual sandwiches to serve.