Place butter, thyme and bag leaf in bottom of 6 quart slow cooked. Add sliced onions, sprinkle with sugar. Cover and cook on high for 8 hours.
Remove thyme and bay leaf discard.
Add stock, red wine vinegar, salt & pepper. Cover and cook on high for 30 minutes.
(See freezing instructions below)
Baguettes
Preheat broiler to high
Arrange bread in a single layer on 2 baking sheets. Broil 30 seconds per side.
Place 1 cup soup in ramekins or oven safe bowls. Top with bread slice and 2 Tbsps. Of cheese.
Place bowls on cookie sheet and broil 2 minutes until cheese is melted.