Heat the butter in large pot over medium heat. Add onions and garlic (thinly sliced), reduce the heat at cook for 1-1,5 hrs until golden brown (stirring often).
Add flour and keep stirring, then add 150ml ov vegetable broth. Stir for 5-10 minutes.
Add 1,5 l of vegatble broth, salt and pepper and let if simmer for 20-25 minutes.
Cook bread with a toaster.
Preheat the oven 365F.
Place the bread slices, topped with cheese and bake until cheese is melted.