How do you make homemade mayonnaise? Did you know mayonnaise is possibly named after Mahon, the capital city of Minorca?
It's not difficult if you're willing to put the strain on your arm. Take an egg yolk, and beat some salt, sugar and (if desired) spices into it with a whisk. In a separate bowl, mix a couple tablespoons each of lemon juice and white wine vinegar. Beat half of that into the egg. Then whisk the egg mixture vigorously while adding a few drops of oil (I like olive, but it gives the mayo a very pungent taste; use safflower for a milder, more classic taste) until it gets thick (this will signify you are getting an emulsion). Then slowly add half a cup of oil while whisking. Whisk in the remainder of the vinegar mixture. Whisk in another half cup of oil. Done. Delicious, but doesn't keep that long You can probably do this with a whisk attachment on a power mixer, but I like the old fashioned way.
Just to add to what I said last night, now that I have a bit more time, and am not on my phone: It's waaaay simpler than ketchup, but a bit more complex than pesto, to give some context. I've never tried making my favorite condiment, mustard, but that's mainly because I don't think that I could make better mustard than some of the stuff I can get at the store. I don't like store bought ketchup or mayonnaise even slightly (and I wouldn't buy salad dressing at a store if they paid me). Once you've had the homemade version, you'll never go back to the dark ages. I think for this challenge I'll make some kind of crazy awesome sauce, then put it on something really simple like eggs benedict.