You can buy this in health food shops - even in some supermarkets. If you live in Central Asia however and you fancy a bit of tofu mayonnaise you have to make it yourself. I haven't really mastered this recipe yet and I'd welcome any suggestions for improving it. The mayonnaise I make never seems to be as light as the stuff from the shops and the ingredients usually separate when I mix the mayonnaise into a salad - I think this is essentially an emulsification issue - but here's the recipe anyway. The quantities given will make about 100 grams or so.
Cream the tofu with a pestle and mortar then transfer it to a bowl for mixing. Add the lemon juice and mix it in. Add the oil gradually. One dessert spoon at a time should be okay - beat it into the mixture before adding the next lot. Beat in the water a dessertspoon at a time and add the salt at the end.
Note: I've since been advised that adding a little lecithin to the mix stops the ingredients separating, though I haven't tried it yet.