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. If using a food processor, use the plastic blade if you have one, as it seems to make a slightly lighter sauce. Egg white is needed in machine-made mayonnaise. Beat 1 egg well with a fork to blend the yolk and white, let it settle a few seconds, then measure. This recipe can be doubled, in which case, just use 1 large egg.
Combine in a blender or food processor:
      2 tablespoons well-beaten egg
      1 large egg yolk
      1/4 teaspoon dry mustard or Dijon mustard
Process on high speed until well blended, about 5 seconds in a blender, 15 seconds in a food processor fitted with the plastic blade, 30 seconds in a food processor fitted with the steel blade. Scrape down the sides, then sprinkle the mixture with:
      1 teaspoon fresh lemon juice and/or white wine vinegar, or 1 teaspoon rice vinegar
      1/4 teaspoon salt
Process for about 2 minutes in a blender, 15 seconds in a food processor fitted with the plastic blade, 7 to 8 seconds in a food processor fitted with the steel blade. Have ready in a small spouted measuring pitcher:
      3/4 cup oil, at room temperature
With the machine running, add the oil in the thinnest possible stream. After about one-third of the oil has been added—the mixture will have swollen and stiffened—add the oil in a slightly thicker stream. Stop the machine when all has been added and scrape down the sides and around the blade, mixing in any unabsorbed oil. If you want a thicker sauce, add as before:
      Up to 1/4 cup oil, at room temperature
Should the sauce be too thick, add as needed:
      Light cream, heavy cream, milk, or water, at room temperature
Transfer the mayonnaise to a bowl and stir in:
      1 tablespoon yellow mustard or Dijon mustard
      1 1/2 to 3 teaspoons fresh lemon juice or white wine vinegar
      Salt and ground black pepper to taste
Serve immediately, or refrigerate in a covered jar for 1 to 2 days.