Heat butter and olive oil in small Dutch oven or medium saucepan set over medium-low heat. Add onions, pepper and sugar. Cook, stirring frequently, 30 to 40 min. until onions are golden brown.
Increase heat to medium. Stir in thyme. Cook, stirring, 2 min. Slowly stir in wine; bring to a simmer. Cook 3 to 5 min. until slightly reduced. Pour in beef broth and bring to a boil. Reduce heat to medium-low. Simmer uncovered 20 to 25 min. to combine flavours.
Place 2 oven-proof soup crocks on a baking sheet. Fill crocks 3/4 full with soup. Top each with a baguette slice, place 2 slices of cheese on each piece of bread. Broil 2 to 3 min. until cheese is melted and bubbly. Sprinkle with chives to serve.
Substitute red wine with white wine.
Cook onions to a rich brown; the darker the colour, the deeper the flavour.
Place leftover soup in zip topped plastic bags and freeze for up to 30 days.