Crockpot French onion soup

I just realized that French onion soup is another great use for stale bread.

Slice those stale restaurant rolls in half, cover them with gruyere cheese, and set them afloat on top of a bowl of French onion soup.

Even better, a bowl of crockpot French onion soup, which required exactly three minutes of effort on my part (largely to slice the onions).

4 thinly sliced onions
3 garlic cloves, minced
4 tablespoons butter
2 tablespoons balsamic vinegar
2 tablespoons brown sugar
3 tablespoons flour
Enough broth to float it all (beef broth would be best; but I used vegetable and it was fine)
Thyme
Salt and pepper
Stale bread and gruyere (or swiss) cheese

Set the crockpot on high, then add the onions, garlic, butter, vinegar, sugar and some salt. Stir together, cover and cook for 1 hour, stirring occasionally. Add the flour, stir thoroughly and let sit for 5 minutes. Add the broth, thyme and pepper, turn heat to low, cover and cook for 6-8 hours.

Cover the stale bread with cheese and pop into the toaster oven until it's all gooey. Float a piece of cheese bread on each bowl of soup.