Process yolks, mustard, lemon juice, and garlic in food processor until combined, about 10 seconds.
With machine running, slowly drizzle in vegetable oil, about 1 minute.
Transfer mixture to medium bowl and whisk in water.
Whisking constantly, slowly drizzle in olive oil, about 30 seconds.
Whisk in salt and pepper.
Refrigerate in airtight container for up in 4 days.
June 17, 2009 Made with Bea. It is delicious. I one-and-a-halved the recipe and we ate the whole thing for dinner on a potato tortilla. Everyone loved it. Recipe from Cook’s Illustrated, July & August 2009.