In a large stockpot on medium-high heat, saute the onions with the butter and bay leaf for 20 minutes, until the onions turn a rich golden brown color.
Deglaze the pan with the sherry and brandy and simmer uncovered for 5 minutes.
Add the white wine and simmer uncovered for 15 more minutes.
Add the beef and veal stocks plus salt and pepper.
Bring to a boil, then simmer uncovered for 20 minutes.
Remove the bay leaf, taste for salt and pepper, and serve hot with grated Parmesan.
