Saute until the onions begin to brown, about 10 minutes, then lower the heat and continue cooking until the onions are lightly browned, about 30 minutes.
Add the wine and cook until reduced by half, about 5 minutes.
1/2 cup dry white wine
Increase the heat to high, add the stock and water, and bring to a boil. Reduce the heat and simmer covered for 30 minutes.
2 cups beef stock, 2 cups water
To serve, place a slice of toasted bread in each bowl, ladle the soup over the bread.