Melt 3 tablespoons of the butter and the oil in a large heavy pot over medium-low heat. Add onions, cover and cook, stirring occasionally, until soft and translucent, about 20 minutes. Increase heat to medium-high, uncover, and add the sugar and season to taste with salt. Saute stirring often until onions are very soft and deep golden brown. Reduce heat to medium, sprinkle in flour and cook, stirring constantly for 2 to 3 minutes. Add about 2 cups of stock and stir to blend, then add remaining 6 cups of stock and the wine. Season to taste with salt and pepper and simmer for about 30 minutes. Adjust seasoning to taste. Preheat oven to 425 degrees. Meanwhile, slice the bread into at least 8 thick slices. Butter both sides of the bread with the remaining 3 tablespoons of butter, then toast until golden brown on both sides in the oven. Place a slice of toast in each of 8 ovenproof bowl, then fill bowls with the onion soup. Spread a thick layer of cheese on top of soup. Set bowls in 2 baking pans, place in the oven and bake until cheese has browned.
Recipe courtesy of Coleman Andrews, Saveur Magazine