There are almost endless possibilities for variation here. Potatoes are my favorite thickening agent for garlic soup, but it can also be thickened with a roux of flour and butter or with bread, the traditional choice in the South of France, where this dish is a specialty. Onions and scallions can be used instead of leeks, although the soup won’t have the same subtle taste. If you use the leeks, include most of the green leaves.

Poultry or meat stock gives the soup more body and flavor, although it’s good made with water. I have purposely kept the soup simple, but for a party, you could enrich it by adding a cup of light cream at the last minute.

• 1/4 cup olive oil
• 2 medium leeks, trimmed (leaving most of the green), split, washed, and sliced
• 12-15 garlic cloves
• 7 cups homemade chicken stock or low-salt canned chicken broth
• 2 pounds potatoes, peeled and cut into 1-inch cubes (about 4 cups)
• 1 teaspoon salt, or to taste
• 2 cups cubed (1/2-inch) firm-textured white bread
• 2 tablespoons unsalted butter

• Heat 2 tablespoons of the oil in a heavy pot. When it is hot, add the leeks and garlic and cook over medium heat for about 2 minutes, until the vegetables begin to soften. Add the stock, potatoes, and salt and bring to a boil. Cover, reduce the heat, and boil gently for 30 minutes.
• Meanwhile, heat the remaining 2 tablespoons oil in a large skillet. When it is hot, add the bread cubes and sauté, stirring almost continuously, until they are evenly browned on all sides. Remove with a slotted spoon and set aside.
• When the soup is cooked, push it through a food mill. Stir the butter into the hot soup and serve with the croutons.