Melt the butter in a large stock pan over low heat.
Peel and thinly slice the onions.
Add the onions to the melted butter. Stir to coat them in butter.
Cover the pan and let cook for 1 ½ to 2 hours, stirring every fifteen minutes.
When the onions have cooked down and are very soft and tender, sprinkle them with 1 tbsp sugar and bring the heat up to medium. Cook, stirring often, until the onions are golden brown.
Add 2 cups of red wine to the pan and 4 cups of beef stock.
Bring to a boil, reduce the heat and cook at a low simmer for another hour. Add more wine and/or stock to taste and let cook for another 30 minutes.
Soup can be cooled at this point and stored in the refrigerator.
To serve: slice and lightly toast two pieces of baquette (2” thick) per serving.
Slice the Jarlsberg cheese into thin slices
Heat the oven broiler to medium high.
Bring the soup to a full boil and ladle into French onion soup crocks.
Top with the baquette slices and cheese and cook under the broiler until the cheese has melted and browned.