If you asked me, I would say that she is the queen of all sauces. Eggs, oil, water, magic!
What is a BLT without mayonnaise? Sad. A sad, albeit bacon-y, sandwich.
My grandmother used to slice tomatoes and put a dollop of mayonnaise on them, top with fresh cracked pepper for a late summer afternoon snack. (Actually, she used Miracle Whip, which is an abomination - she also frequently used margarine, bless her soul. I use Hellman's in my version, but I must tip my hat to grandma for the idea.)
I will say it again - Miracle Whip is an abomination and woe onto you if you use the stuff!
Chowbacca!'s writers have chimed in on our various favorite store brands (I'm a Best Foods/Hellman's guy), but the real deal is home made.
A few words on the science of emulsions, if you don't mind.
Just about anyone with an IQ above room temperature will tell you that oil and water do not mix. Why that is has to do with their molecular composition.
To emulsify is to suspend one phase (liquid or water) throughout another, unlike phase (oil, or lipid).
If you have ever watched oil floating on water you know that when one blob of oil comes into contact with another they immediately merge, forming a larger blob.
This is not unlike watching a Lava Lamp (which is a lipid, wax, suspended in a liquid phase, usually glycerine).
A little molecular elbow grease must be employed to keep the oil in mayonnaise from coalescing into a giant blob (this is what we mean when we say a "broken" emulsion). The muscle of the operation is a sneaky molecule called a phospholipid: lecithin.
Lecithin is a molecule that exists abundantly in nature. There is some in the yolk of an egg, and there is quite a bit in the ground up seeds of the mustard plant.
Like all phospholipids, lecithin is a molecule that has a hydrous or hydrophilic end (the phosphate end) and a hydrophobic end (the lipid end).
The hydrophobic end is naturally attracted to fats, the hydrophilic end is soluble in water. When agitated, the fat phase of an emulsion is broken up into tiny globules which become surrounded by phospholipids bound up at the hydrophobic end, holding liquid water in suspension around each globule. The oil globules are thus prevented from coming into contact with one another "et voila", you have a stable emulsion.
Of course, if you want to find out more about this phenomenon you owe it to yourself to watch Alton Brown explain it. Better still, go out today and buy a copy of Harold McGee's "On Food And Cooking: The Science And Lore Of The Kitchen".
Everyone should have a copy in their kitchen.
And now, watch me goof off and with one hand tied behind my back (actually, it's holding the camera), successfully build an emulsion using a lot of science and maybe just a little luck: