You mash two or three cloves of good garlic — I like the purple-skinned Rose de Lautrec, or whatever it's called — with good sea salt; then add a handful of pine nuts and work it into a smooth paste.
Then you add the basil leaves — no stems! no blossoms! — and keep mashing, mashing, mashing. If you're lucky you get a nice smooth paste. I didn't, not tonight; the basil was too wet. It's best to use basil leaves straight from the garden (or market), not from the refrigerator; and it's certainly best not to wash it; you can never get it dry enough after washing it. But I did, today.
Oh well: good enough for Thursday dinner. We like pesto on fusili, whose spiral threads hold the sauce nicely once you stir it all up with your fork. But you can see it wasn't mashed smooth enough.