Sauté onion in the melted butter over low heat.
Cook until onions are clear. Do not brown. Slowly add
the flour, stirring and cooking to make a blond roux (approximately
seven minutes).
Add in beef stock and spices, bring to a boil, then
lower heat and simmer for five minutes. Remove pot from heat. In a
small bowl, beat egg yolk and cream together while adding in a little
of the soup. Add this mixture to the pot.
Mix thoroughly. Place one slice of toasted French bread in the
bottom
of individual serving crocks. Sprinkle Romana cheese on the
bread.
Ladle soup on top of bread. Place a slice of mozzarella on top of
soup,
letting edges rest on top of the crock. Sprinkle bread crumbs
lightly on top of the
cheese. Broil just until cheese is bubbly and lightly browned. Serve
immediately.