“If onions were as rare as truffles, chefs would pay dearly for them,” said Michael Ruhlman in Ruhlman’s Twenty (Chronicle Books). This humble and ubiquitous vegetable is a “miracle ingredient” that adds both sweetness and savoriness to a dish while seeming to unify the flavors of other ingredients. Perhaps these traits even explain why the word onion derives from the Latin term for “one, oneness, or unity.”

The onion is such an important tool in cooking that I count knowing how to tap its various effects as one of the 20 fundamental techniques of the contemporary kitchen. “Used raw, onions have one effect on a soup or sauce or stock.” But heat dials up their sweetness, and an onion contributes different nuances depending on whether it’s lightly sweated, thoroughly sweated, browned, or roasted.

For a traditional French onion soup, no stock or broth should be used, just water and a bit of sherry. The amazing flavor—“at once sweet, savory, and nutty”—comes from slow-cooking the onions for hours. If time is an issue, increased heat can speed the process if you stir vigilantly to avoid burning. The reward is an economical dish that “may be one of the best soups in the Western canon.”

Recipe of the week
Traditional French onion soup
1 tbsp butter
7 or 8 Spanish onions, thinly sliced
Kosher salt
Freshly ground black pepper
6 to 12 slices of baguette or any country-style bread
¹/³ cup sherry
Red or white wine vinegar (optional)
Red wine (optional)
½ to ¾ lb Gruyère or Emmentaler cheese, grated

Use a large pot that will hold all the onions (a pot of enameled cast iron provides the best surface). Place pot over medium heat and melt the butter. Add onions, sprinkle with 2 tsp salt, cover, and cook until onions have heated through and started to steam. Uncover, reduce heat to low, and cook, stirring occasionally (you should be able to leave onions alone for an hour at a stretch once they’ve released their water). Season with several grinds of pepper.

At any time before onions are ready, preheat oven to 200 degrees. Place bread slices in oven and let them dry completely.

When onions have completely cooked down, water has cooked off, and onions have turned amber—this will take at least a few hours—add 6 cups of water. Raise heat to high and bring soup to simmer, then reduce heat to low. Add sherry. Taste and season with salt and pepper as needed. If soup is too sweet, add some vinegar. If you would like a little more depth, add a splash of red wine. If you prefer a more delicate soup, add an extra cup of water.

Preheat broiler. Portion soup into ovenproof bowls, float bread on top, cover with cheese, and broil until cheese is melted and nicely browned. Serve immediately. Serves 4 to 6.