Tahini from a jar is, I find, palate-coating, like a savoury form of peanut butter. It gives hummus a sludgy, adhesive quality. Making your own tahini is not complicated. There are two ingredients.
Recipes tell you to put the sesame seeds on to a baking sheet in a gas mark 4/180C oven for 10 to 15 minutes, stirring them every so often to make sure they do not brown. It is easier to cook them in a heavy saucepan over a low heat -- but you have to stir them regularly, and to recognise the point after which they will be overcooked. Toasted sesame seeds, delicious in a salad, are bitter in a tahini sauce.
I have a small, electric mill -- similar to what Delia Smith calls a mini-chopper. When the seeds are cool, I whizz them in the mill with sunflower oil. The standard ratio is about 4 parts sesame seeds to 1 part, or slightly more, of oil. It is a good idea to add the oil a little at a time, until you get the consistency you want. You need to whizz the mixture thoroughly -- and you are unlikely to get a completely smooth result.