To your food processor, add whole egg and egg yolk. Blend for 30 seconds.
Add lemon juice, mustard powder and salt. Blend for 30 seconds.
Turn food processor on and in a slow steady stream add, vegetable oil while food processor is running until all oil has been slowly added. If you are using a mini food prep food processor, slowly add oil to top lid of food processor where holes are. The oil will slowly drip through the holes. When oil drains, refill and keep adding oil until you have used up all the vegetable oil. Taste for seasoning and adjust accordingly.