Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
  1         tablespoon  fresh lemon juice
  1         tablespoon  sherry vinegar -- (available at
                        -- specialty foods
                        -- shops and some
                        supermarkets)
  1           teaspoon  dijon-style mustard
  1                     garlic clove -- minced
     1/2      teaspoon  sugar
     1/4           cup  olive oil -- (preferably
                        -- extra-virgin)
  2 1/2         pounds  -- (about 6 medium)
                        -- tomatoes, cored and
                        -- cut into
                        -- 1/2-inch-thick
                        slices
     1/2           cup  thinly sliced red onion -- separated into
                        -- rings
  2                     shallots -- sliced thin
     1/3           cup  minced mixed fresh herbs such as basil -- parsley, tarragon,
                        -- and/or mint
                        plus an herb sprig for garnish

Preparation:

In a small bowl whisk together the lemon juice, the vinegar, the mustard, the garlic, the sugar, and salt and pepper to taste, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. Arrange the tomato slices on a deep platter, scatter the onion and the shallots over them, and pour the dressing over the salad. Chill the salad for 20 minutes, sprinkle it with the minced herbs, and garnish it with the herb sprig.