For cold poultry, meats, fish, and strong-flavored vegetables; traditional with cracked crab. Yellow mustard is lightest and best for fish and seafood; stronger Dijon suits poultry and meats. Use a ceramic, glass, or stainless-steel bowl—aluminum or copper will react with the acid and affect the color and even the flavor of the sauce.
Whisk together in a medium bowl until smooth and light:
      2 large egg yolks
      1 to 2 tablespoons fresh lemon juice or white wine vinegar
      1/4 teaspoon salt
      Pinch ground white pepper
Whisk in by drops until the mixture starts to thicken and stiffen:
      1 cup vegetable oil, at room temperature
As the sauce begins to thicken—when about one-third has been added—whisk in the oil more steadily, making sure each addition is thoroughly blended before adding the next. Should the oil stop being absorbed, whisk vigorously before adding more. Stir in:
      1 tablespoon yellow mustard or Dijon mustard
      Salt and ground black pepper to taste
Serve immediately or refrigerate in a covered jar for 1 to 2 days.