In a food processor (or possibly with a stick blender) blend 1/4c oil with egg, mustard seed, garlic, and salt for 30 seconds. Slowly add remaining oil while continuing to blend. Mixture should emulsify to a thick consistency. Add lemon juice and blend for 10-15 seconds. Voila!
I used garlic scapes in lieu of garlic for this batch. I’ve also added chipotle pepper in Adobe sauce for a smoky tasty kick. Just watch how much additional liquid is added since a looser consistency may result. Note: it’s best to add options after emulsification has happened.