Before starting, be sure all ingredients are room temperature.
To the bowl of a food processor, add the egg. Turn the processor on low for 20 second.
Add the dijon, lemon juice, and salt. Process on low for 30 seconds.
SLOWLY add the oil, with the processor running on low. Do not rush this step. Once the oil is completely combined, you will notice the mixture begin to look like mayonnaise. Scrape down the sides of the bowl, and run for an additional 10 seconds once it looks like mayo.
Store in an airtight container in the fridge, enjoy!