Step 1

Take the egg and mustard out of the refrigerator and let rest at room temperature for at least 30 minutes to facilitate emulsification and ensure a firm mayonnaise.

Step 2

In a big bowl, combine the egg yolk, mustard, a pinch of salt, a pinch of pepper, and a few drops of vinegar. If you can, use a stand or electric mixer with a bowl or an immersion blender with a wide-mouth Mason jar. If using an electric mixer, hold the beaters at an angle to the bottom of the bowl to facilitate emulsification. Begin to beat at the highest speed, continuing until the contents of the bowl are completely combined. With the beaters running, begin to SLOWLY add the oil, drop by drop at first and then in a slow, steady, thin stream. Stop adding oil but keep beating. You should soon see the mayonnaise "take," that is, begin to look like thick mayonnaise and not like an oily liquid. When this happens, you can resume adding the oil in a thin stream, still beating, but never add a large amount at once. This could cause the emulsion to liquefy.

Step 3

Taste. If the mayonnaise needs salt, do not add salt directly, for the sauce will not be able to absorb it. Instead, put a pinch of salt in a bowl and add a bit of vinegar, about half a teaspoon. Dissolve the salt in the vinegar and then stir it into the mayonnaise.

Step 4

Your mayonnaise is ready and will keep, covered or stored in a Mason jar with a lid, for a few days when stashed in the back of the refrigerator.