Homemade mayonnaise: it's a good thing.
You'll need:
- Three eggs
- Oil (I use bog-standard canola oil. Feel free to substitute olive oil or any other standard cooking oil).
- A lemon
- Mustard (I have a weakness for Expensive Imported Gourmet Mustard)
- Salt and pepper
- A blender of some sort -- either a standard stand-alone blender with a big glass jar or one of these small hand-held immersion blenders (often referred to as "The Stick"). Actually, Stick blenders work really, really well for making mayo. You just have to watch out for how they have a habit of making a huge mess. Don't use a food processor. You'll regret it (and I'm pretty sure that it won't work, anyway).
Separate the eggs. You can do what you want with the whites (whip them in to a meringue or throw them out -- it's irrelevant for our purposes here). Put the yolks in the mixing container. Add the juice from the lemon (don't use bottled juice -- fresh is so much better -- and definitely don't use any sort of lemon juice intended for consumption as part of a mixed drink (i.e. Rose's). Add about a teaspoon of mustard (keep the mustard around -- you'll probably want to add more later). Start blending at low speed. Start adding the oil slowly. When it starts to stiffen, it'll stiffen very, very quickly.
Once it's started to thicken, add more mustard/lemon juice/salt/pepper to taste. If it gets too stiff, you can either drop another egg yolk in or thin it by adding lemon juice/water (if you really don't know what to do with the left over egg whites, you can use those to help thin out a too-stiff sauce).
With practice, you can get the process down to 5 minutes.
You can play with the ingredients and proportions for different flavors and purposes. For example, you can add roast garlic and use olive oil as your oil to make aioli. Or you can load it up with extra mustard for a sauce that works really, really well with fish. I've even seen recipes that call for adding saffron (have to try that one day).
After tasting homemade mayonnaise, you'll find that the pale stuff out of the jar doesn't really compare. The only problem is that homemade mayo doesn't keep well -- a few days at most.