Whisk together orange zest, orange juice, lemon juice, Dijon mustard, salt, and pepper. Gradually whisk in olive oil until well blended.
Try This Twist! Grapefruit Vinaigrette: Omit orange zest and lemon juice. Substitute grapefruit juice for orange juice. Proceed as directed, whisking in 1 Tbsp. honey with juice. Serve over green salad, grilled fish, baked chicken, or steamed green beans.