1- Use a small bowl attachment for a food processor if you have one, or go with an immersion blender in a tall jar for ease.

2-For the food processor method: Add the egg and process for 20 seconds, then add mustard, vinegar, and salt and process for another 20 seconds. Scrape the sides, turn it on, and slowly drizzle in the oil drop by drop at first.

3- Once it thickens, keep adding the oil in a steady stream until it’s all mixed in, then process for 10 more seconds and taste to adjust with salt or lemon juice.

4-If using an immersion blender: Put the egg, mustard, vinegar, salt, and lemon juice into the jar, pour the oil on top, and blend at the bottom until it starts to thicken after 15-30 seconds. Then, move the blender up and down to fully incorporate everything.

5-For the hand whisk method: Whisk the egg, mustard, vinegar, and salt in a bowl until blended, then add the oil drop by drop while whisking constantly until it thickens, followed by the rest in a thin stream.

6- Finally, taste and adjust the seasoning, then store it in the fridge for at least an hour to let the flavors settle.