Cut onions in half and slice with grain about 1/8-inch thick.
Melt butter and add sliced onions. Saute slowly for 20 minutes, stirring frequently.
Add paprika, pepper, bay leaves and flour. Mix well, keeping flame low. Stir while cooking for 5 minutes.
Gradually add hot bouillon while stirring, preferably with a wooden spoon.
Simmer soup covered for 30 minutes (at least).
If a rich brown coloring is desired, add caramel coloring. Taste soup and season with salt.
Fill crocks. Top with thin slices of french bread and cover with 1 1/2 ounces of grated swiss cheese. Place under broiler and melt cheese until golden brown.
Notes
Salt can be omitted if using beef bouillion cubes.