3 tbsp. butter
3-4 large red onions (about 3 lbs.)
1/2 tsp. kosher salt
1 cup white wine
1 tbsp. dry sherry
1 tbsp. flour

  • melt butter in a dutch oven, add onions and salt, and stir
  • cover and let onions soften for 5 minutes
  • remove cover and let onions carmelize until golden brown, stirring occasionally, which may take 45-60 minutes
  • add wine and sherry to the pot and bring to a boil
  • stir in flour and let thicken for 1-2 minutes

2 quarts beef stock, warmed
1/2 tsp. pepper

  • add stock and pepper to onions and bring to a boil for 10 minutes
  • adjust salt and pepper, to taste

8-12 slices of french bread
4-6 oz. gruyère, grated

  • ladle soup into ramekins, top with bread and cheese, and broil 1-2 minutes, until cheese is melted and browned

source: https://cooking.nytimes.com/recipes/1017256-french-onion-soup