I just made a batch this afternoon! I start from scratch, since prepared garbanzos aren't available here. It's 1 cup dry garbanzos, soaked overnight and then simmered until soft (sometimes I add a bay leaf and salt, but often I just simmer them plain). That yields 2 to 2.5 cups of cooked garbanzos, so you could just start with that. Either way, save about a half cup of the cooking liquid (or canned liquid) in case you need to thin out the hummus.
Put the prepared garbanzos in a food processor with the following:
1/3 cup tahini (stir well before measuring it out)
1/3 cup fresh lemon juice
3 tablespoons olive oil (about half the 1/3 cup measure)
2 cloves garlic
1/2 teaspoon ground cumin
cayenne or chili powder to taste
salt and pepper to taste
I only use a couple cloves of garlic, as the raw garlic gives it a lot of heat and can dominate the flavors. However, I often add as much as a head of roasted garlic--or maybe roasted red pepper or sun dried tomatoes or a handful of basil or whatever to vary the flavors. So yummy!