When my daughter was a child, she loved a bubbling bowl of cheese-crusted onion soup better than almost anything. For her, I made it without wine. The idea of using Champagne comes from the legend that onion soup was invented by Henri IV one early evening after a hard day’s hunting. He was supposed to have stopped at a peasant hut and asked for something to eat. Embarrassed, the wife replied that she had nothing but onions, some stale bread, and a little fat in the house. The king replied that he would make a soup using the Champagne that he had left.

I would use Champagne only if I had some left and getting flat after a party. (Onion soup is a famous hangover remedy.) Usually, I would substitute a somewhat acid white wine—no sweetness, since the onions are so sweet. Any single stock can be used, although I like the balance of beef and chicken. Country people often made this just with water. I remember Jacques Pepin once making a soup (in A French Chef Cooks at Home) where he broke the crust of a soup that was almost solid with layered bread and sliding in a ladle filled with egg yolks and Port and swished it around in the soup. Vary at will.

There are pale onion soups, but for this one, it is important to cook the onions slowly so they get very dark but do not burn. When the pan is deglazed, the caramelization, a coating on the onions, comes off into the liquid, leaving the onions clear and the soup very dark. The pan must be large enough so that the onions glaze rather than stew in the juices.