You add the butter to the dry ingredients before adding the liquid ingredients. (beantownbaker.com)
And for the flavor, you could try taking it up a notch by adding some liquid smoke. (connoisseurusveg.com)
After your mayonnaise base (oil + egg + salt) comes together, then add your liquid ingredients like the whey, vinegar, lemon juice, etc.. (mommypotamus.com)