Step 1Whisk the egg yolks in a medium bowl until light and airy. Begin adding the oil, a drop at a time, until the mixture begins to lighten. Continue adding the oil, at a slow drizzle, whisking constantly.
Step 2When a third of the oil has been added, start adding the lemon juice, a little at a time, to thin out the mayonnaise. Continue adding the oil a little at a time until it is all incorporated, whisking constantly. If the mayonnaise is too thick, add water a little at a time to thin it. Stir in the lemon zest. Season to taste with salt, and refrigerate until needed.