Whiz all the ingredients except the oil in a food processor on a low speed for 30 seconds. With the motor running (still on low), very slowly drizzle in the oil until the mayo is thick and smooth. (Did I mention to drizzle it very slowly? You want it to pour in a very, very fine stream, otherwise it won’t form an emulsion.) If you included the whey, cover the mayonnaise and let it sit at room temperature for 8 hours before refrigerating. This activates the enzymes in the whey. If you didn’t use whey, refrigerate immediately.
This recipe lists whey as an optional ingredient. Mayonnaise made with whey will keep for 2-3 months longer than mayonnaise made without, which normally only lasts 2-3 weeks. You can use the whey that is left over from making your own Cream Cheese. If you don't have any whey that's fine, but use up the mayonnaise within a week or two.