Regular or light mayonnaise can be used in this recipe. Do not use blackstrap molasses. You can substitute toasted hazelnut or walnut oil for the extra-virgin olive oil.
Combine mayonnaise, molasses, mustard, and salt in 2-cup jar with tight-fitting lid. Stir with fork until mixture is milky in appearance and no lumps of mayonnaise or molasses remain. Add vinegar, seal jar, and shake until smooth, about 10 seconds.
Add ¼ cup olive oil, seal jar, and shake vigorously until thoroughly combined, about 10 seconds. Repeat, adding remaining ¼ cup olive oil and vegetable oil in 2 additions, shaking vigorously until thoroughly combined after each addition. (After third addition, vinaigrette should be glossy and lightly thickened, with no pools of oil on its surface.) Refrigerate for up to 1 week. Shake briefly before using.
