Tangy, light and refreshing, this vinaigrette is served over simple greens at most cafés in Paris. You can adjust the amount of mustard and vinegar to your liking, but this is the ratio that I enjoy the most. Also, feel free to add freshly chopped herbs like chives or parsley to the dressing if available to you.
While this recipe only has tomatoes and lettuce in the salad, the dressing works wonderfully with avocado, hearts of palm or chickpeas.
In a small bowl, whisk the mustard, oil, and vinegar together. Season with salt and pepper to taste, adding any fresh herbs here if desired. Place the lettuce and tomatoes in a serving bowl and toss with the dressing, being careful not to bruise the lettuce.