Here's the recipe I use, sort of. I don't add cognac, usually use very dry red wine (or no wine), and I don't really measure the ingredients:
I just use yellow or white onions, whichever is cheaper. It sometimes turns out a little too sweet, so I never use the big "sweet onions"
French Onion Soup
From The Way to Cook, Julia Child, Alfred Knopf, 1989.
ISBN 0-394-53264-3
3 Tbsp. butter
1 Tbsp. light olive oil or fresh peanut oil
8 cup thinly sliced onions (2 1/2 pounds)
1/2 tsp. each salt and sugar (sugar helps the onions to brown)
2 Tbsp. flour
2 1/2 qt homemade beef stock, at least 2 cups of which should be hot
4 to 5 Tbsp. cognac, armagnac, or other good brandy
1 cup dry white french vermouth
This is certainly one of the all-time favorites. The canned and packaged onion soups I've tried have been very good, and the only way to better them is for you to have your own beautiful beef stock. However, bought onion soup will benefit from the flavor additions suggested here. TIMING: For most delicious results, you want a slow simmer for 2 3/4 to 3 hours.
A food processor with slicing blade or a hand slicer is useful for the onions; a heavy-bottomed 3-quart saucepan with cover for onion cooking and simmering.
Browning the onions - 40 minutes. Set the saucepan over moderate heat with the butter and oil; when the butter has melted, stir in the onions, cover the pan, and cook slowly until tender and translucent, about 10 minutes. Blend in the salt and sugar, raise heat to moderately high, and let the onions brown, stirring frequently until they are dark walnut color, 25 to 30 minutes.
Simmering the soup. Sprinkle in the flour and cook slowly, stirring, for another 3 to 4 minutes. Remove from heat, let cool a moment, then whisk in 2 cups of hot stock. When well blended, bring to the simmer, adding the rest of the stock, the Cognac or brandy, and the vermouth. Cover loosely, and simmer very slowly 1 1/2 hours, adding a little water if the liquid reduces too much. Correct seasoning.
May be prepared in advance; chill uncovered, then cover and refrigerate or freeze.
Serving. Serve the soup as it is, accompanying it with French bread and a bowl of grated Swiss or Parmesan cheese, or gratine it. Makes about 2 1/2 quarts, serves 6.
