Melt 1/4 cup butter in saucepan and fry onion in this until golden brown but not burnt.
Add the flour and sugar and stir over low flame until brown.
Add the stock and season with salt.
Stir over low heat until it boils; then leave to simmer slowly for 10 minutes.
Butter and toast the sliced bread and put into the Soup tureen.
When toast rises to the top, sprinkle liberally with grated cheese and run under boiler for a few minutes to melt the cheese.
Alternately, the toasted bread may be floated in individual oven-proof dishes, then sprinkle with grated cheese and run under the broiler.
Yield: 5 servings.