This following recipe is what you would call a back-pocket recipe — something you can store away in your brain and pull out whenever you need it without ever actually looking back at the recipe. It is simple, bright, balanced, flavorful, and most importantly it goes well with almost any salad.
In a bowl, combine mustard, vinegar, garlic, and shallot. Whisk to combine. Then, slowly pour in the oil in a steady stream while whisking vigorously. If the oil starts to pool or show up in droplets, stop adding oil and whisk until completely integrated before starting again.
Taste, and season with salt and a generous amount of freshly cracked pepper. You want the dressing to be bright and sharp in flavor. Serve over any salad.