1 T wine vinegar or lemon juice
1.5 tsp minced onion
½ tsp mayo
½ tsp mustard
salt and pepper
3 T olive oil
Whisk first 5 ingredients until milky in appearance and no mayo lumps remain. Place oil in a small measuring cup so that it is easy to pour. Whisking constantly, very slowly drizzle oil into vinegar mixture. If pools of oil gather on surface, stop adding oil and whisk well to combine, then continue drizzling and whisking. Showl be glossy and slightly thickened. Refrig up to 2 weeks, re-whisking before use.
From: Editors at America’s Test Kitchen. (2015). 100 recipes: The absolute best ways to make the true essentials. Brookline, MA: America’s Test Kitchen.