Classic Mayonnaise

Whisk 1 large egg yolk, at room temperature 30 minutes, ½ tsp. Dijon mustard, and ¼ tsp. kosher salt in a small bowl until combined well. Add about ¼ cup olive or vegetable oil (or a combination) drop by drop, whisking constantly until mixture begins to thicken. Whisk in 1 tsp. white-wine vinegar or cider vinegar and 1½ tsp. fresh lemon juice, then add remaining ½ cup oil in a very slow, thin stream, whisking constantly until well blended. If at any time it appears that oil is not being incorporated, stop adding oil and whisk mixture vigorously until smooth, then continue adding oil. Whisk in salt to taste and ¼ tsp. white pepper (if using). Chill, surface covered with plastic wrap, until ready to use. Do Ahead: Mayonnaise keeps, covered and chilled, 2 days.