1 1/2 bunches basil
2 cloves garlic
1/3 cup toasted pine nuts
1/2 cup grated parmesan
This is a very flexible recipe. You can pretty much vary the ratio of the ingredients as you like, and feel free to substitute toasted walnuts or pistachios for the pine nuts -- or do a mix of nuts, if you like. I've had good results with all of those. Just be sure to toast the nuts, to develop their flavor. The cheese doesn't have to be parmesan -- a hard asiago or romano would work just as well, and you could of course experiment with other hard salty cheeses. Garlic is a matter of personal preference, so use however much you like, and the lemon juice is just something I happen to like because it adds a nice freshness and it seems to keep the basil in the pesto from oxidizing and turning a yucky color. You do this how you like it.
In a food processor or blender, whiz up the garlic until it's in little pieces, then add the grated parmesan (a food processor can grate the cheese for you, of course), the toasted nuts, and the basil. Whiz the ingredients together and start drizzling in the olive oil. Add as much as you need to get the texture you like. Some people like their pesto with a pastey texture and some like it looser, so I'm not going to tell you how much olive oil to add. When it looks good, add lemon, salt, and fresh cracked pepper to taste. Keep in mind that lemon juice can create a "salty" taste on the tongue, so add them one at a time and taste between additions. The parmesan is salty, anyway, so sometimes you don't need much salt.