In a dutch oven or large pot, heat the pan, then add butter to melt.
Slice up two large onions and slice once down the middle to have medium length onion strings. Add to melted butter. This will need to cook on low - med.low flame for 30-40 minutes. Stirring consistently
Add tablespoon of flour to mixture. Mix together and add in broth. Let simmer for 20-30 minutes. Turn oven to broil.
Ladle soup into small ramekins and place the baguette slices into the soup. Sprinkle cheese to cover the bread pieces.
Place in top rack of oven. Broil until cheese is brown and crispy. Let sit until warm.