Peel and slice onions thinly, around 1/8 inch thick.
Melt butter in a large pot, add onions, and cook for 1.5 hours.
Add pepper, paprika, bay leaf; cook for 10 more minutes.
Pour in broth and wine, and bring to a boil.
Mix flour in broth, add to soup, simmer for 2 hours.
Adjust colour, add salt, and refrigerate overnight.
Reheat in the microwave or stove.
Optionally, pour into oven-safe bowls, and top with bread, and cheese.
Broil for about 5 minutes until the cheese bubbles.
You can freeze any leftover soup for later use.