Toast 6 thick slices of French bread in a 300 degree oven until crisp. Blend the Stilton with a couple Tablespoons of butter, then spread on the toast. When ready to serve the soup, pop one of these on top of each serving bowl and sprinkle with lots of cheddar cheese. Melt butter in a large saucepan over low heat. Add onions, cover, and cook until translucent--stirring occasionally--for about 30 minutes. Add the stock and bring to a boil. Reduce heat and simmer for 15 minutes. Add cream and bring to a boil. Reduce heat and simmer to thicken slightly--about 15 minutes. Season generously with salt and pepper. Ladle into bowls, top with Stilton Toast, and run under the broiler until the cheese is melted and brown.