From around my french table. (But my way!)
1 lg egg yolk, room temperature
2 tsp lemon juice or wine vinegar
1/4 tsp Dijon mustard
1/2 - 1C oil
Put yolk, lemon juice/vinegar, and mustard in the Vitamix with some salt. Whirl to blend. Then drop by drop start adding the first 1/4C of oil. Once that's been beaten in and the mix is starting to look like mayo you can add the remaining oil in a slow stream, as much as needed to get the consistency you want.
Taste, and adjust with salt/pepper, mustard, etc as needed.