Tuna Salad with Cornichons and Whole-Grain Mustard | America's Test Kitchen

Ingredients

• 1/4 cup finely chopped onion
• 2 tablespoons olive oil
• 3 (5-ounce) cans solid white tuna in water
• 1/2 cup plus 2 tablespoons mayonnaise
• 1/4 cup finely chopped cornichons
• 1 celery rib , minced
• 1 tablespoon minced fresh chives
• 1 tablespoon whole-grain mustard
• 2 teaspoons lemon juice
• 1/2 teaspoon sugar
• 1/2 teaspoon table salt
• 1/2 teaspoon black pepper