Peel onions and slice 1/8 inch thick, preferably in a food processor.

Melt butter in a 6-quart (or larger) stockpot. Add onions; cook, uncovered, over low heat for 1 1/2 hours, stirring occasionally.

(The long cooking time makes the onions mellow and sweet.) Stir in pepper, paprika and bay leaf; saute over low heat 10 minutes more, stirring frequently.

Pour in 6 cans broth and wine. Increase heat and bring to a boil.

Dissolve flour in remaining 1 can broth.

Stir into boiling soup.

Reduce heat and simmer slowly for 2 hours.

Adjust color to a rich brown with caramel coloring, season with salt. Refrigerate overnight. To serve, heat soup in microwave or on stove top.

If desired, pour into ovenproof crocks or bowls.

Top with a slice of bread and a sprinkling of grated cheese. Heat under the broiler until cheese melts and bubbles, about 5 minutes.

Leftover soup can be frozen.