This is my go-to vinaigrette, perfect for dressing anything from a simple green salad to earthy French lentils to a platter of grilled vegetables. You can vary it by switching to a different oil or vinegar or by adding fresh herbs or other flavorings. I use sherry vinegar because I like its mellow, rounded flavor and I find it is less harsh and more complex than most red-wine vinegars. My oil choice is usually a moderately priced extra-virgin olive oil with a fruity character. No cough-inducing bitterness typical of a big Tuscan oil, please. I like Unio and Lucini brands, the former from Spain and the latter from Italy.
This vinaigrette can be refrigerated in an airtight container for up to 1 week.
In a small bowl, whisk together the vinegar, mustard, ¼ teaspoon salt, and 1/8 teaspoon pepper. Gradually whisk in the oil, a little at a time, until the sauce is creamy and blended. Taste and adjust the flavor balance and seasoning. Whisk again to blend just before using.
Use 1/2 fresh lemon juice and 1/2 vinegar for the vinegar.
Substitute walnut, hazelnut, or grapeseed oil for all or part of the olive oil.