Ready in 15 minutes? Yes, please!

- 4 Tbsp. unsalted butter
- 3 large sweet onions, divided
- 1 and 1/2 tsp. brown sugar, divided
- salt
- coarse black pepper
- 6 cups low or no-sodium beef broth
- 3 sprigs fresh thyme
- baguette or other white bread
- 5 oz. Gruyere cheese
- 1 cup red wine