Homemade mayonnaise has very few ingredients in it. It's basically a vegetable oil and egg yolk emulsion, so it's all technique. Some would have you believe it's difficult, but it's not. It's just a matter of adding the oil slowly enough...
I used the recipe from David Lebovitz, and I love it. It's silky, garlicky goodness. Delish. (Warning, don't proceed if eating raw egg yolks disturbs you in the slightest).
3 cloves of garlic½ tsp salt
1 large egg yolk
1 cup (250ml) extra-virgin olive oil
Take the egg out of the fridge and warm the egg to room temperature. Room temperature eggs emulsificate more easily. Mash the garlic in a mortar and pestle or food processor until it's properly turned into a paste.
Mix the garlic into the egg yolk, and then *VERY* slowly mix in the oil. EXTREMELY slowly to start, and quite slowly towards the end. If you add the oil too quickly, you will break it - i.e. the oil will separate from the egg yolk, and you'll have globs of egg floating in oil. You don't want that. I took about 5 minutes to add one cup of oil.
Beat in all the oil, then beat in the salt. That's it. You've just made mayonnaise, and it'll be delicious on your sandwiches. Thick. Creamy. Salty. Yum.