In the bowl of a food processor (or blender), combine the egg, salt, dry mustard powder, and 1/4 cup of light olive oil. Pulse ingredients for 30-60 seconds, until all combined and pale yellow in color.
With the food processor running, slowly drizzle in the remaining 1 cup of light olive oil through the processor’s food chute.
Once all of the oil is added and the mixture has emulsified, stir in the juice of 1/2 a lemon, either pulse the food processor or stir by hand to combine.
Keep refrigerated in an airtight container, up to one week.
Recipe Notes
**Cardinal Rule** Be careful when measuring the dry mustard powder. Add too much, and you’ll end up with a strong mustard bite to your mayo. Also — I was not kidding about the light olive oil; it is a necessity!