THREE ONION SOUP

Steps:

• Chop enough white and pale green parts of leeks to measure 2 cups. Wash leeks well in a bowl of cold water. Lift from water and drain in a colander. Heat oil in a 10-inch nonstick skillet over moderate heat until hot but not smoking, then cook chopped leeks, onion, and shallots with salt and pepper to taste, stirring frequently, until edges are golden brown, about 15 minutes. Add 1/2 cup water and deglaze skillet, scraping up brown bits. Transfer mixture to a saucepan.
• Peel potato and cut into 1/2-inch cubes. Add potato, broth, and remaining cup water to onions. Simmer, covered, stirring occasionally, until potatoes are very tender.
• Puré;e 1‚ cups soup in a blender (use caution when blending hot liquids) and stir into remaining soup. Season with salt and pepper.
• Serve soup sprinkled with cheese and drizzled with vinegar.