Brennans French Onion Soup

8 med onions,chopped 11/2 c butter
11/4 c all purpose flour
10 cans of beef stock (or 12 cups homemade)
1Tablsp salt 1/2 tsp. cayenne pepper
2 Tblsp. cream
1 egg yolk
buttered croutons Parmesan cheese

Melt butter in a lg. soup pot; add onions and lower the heat. Cook till the onions are clear---do not brown.
Add flour and cook 10 min, stirring. Add salt and cayenne pepper. Blend in the beef stock, always stirring, and bring to a full boil. Reduce heat and cook slowly for 20 min. Remove from heat. Beat cream and egg yolk together. Add a little hot soup to the mixture, blend, then pour back into soup. If soup becomes too thick, add a little more water. To serve, pour into bowls, add croutons and sprinkle with Parmesan cheese.
Makes 12 servings. Freezes well