Now, you could follow a real recipe like this: https://www.seriouseats.com/recipes/2014/10/simple-vinaigrette-recipe.html But if I just want a quick single serving of salad dressing, this is how I do it. The most important part is the 3:1 ratio of vinegar & oil. And it doesn’t have to be an exact fussy measurement. I start with vinegar, 2 parts neutral oil, 1 part olive oil. The oil will float on top, so it’s easy to eyeball the amount. Then a big dollop of mustard, splash of lemon juice, and a healthy pinch of salt & fresh ground pepper. Seal up the mason jar and shake the hell out of it. Et voila - salad dressing.