Actually, the most basic vinaigrette is made without mustard, but this is a good, all-purpose dressing. For a milder dressing, leave out the garlic.
1tablespoonred wine vinegar, or to taste
1garlic clove, smashed (optional)
Salt and freshly ground black pepper, to taste
2½ to 3tablespoons good olive oil
In a glass measuring cup or small bowl, whisk or stir together with a fork the vinegar, mustard, garlic, and salt and pepper. Slowly whisk in the olive oil until smooth and emulsified or creamy. Taste and correct the vinegar-oil balance. Remove the garlic clove before serving.