The best foundation for pesto is fresh basil (Ocimum basilicum). Without fresh basil this is hardly worth doing and you may as well buy it off the shelf. The best way to insure magnificent pesto is to grow your own sweet basil. Finding good, fresh basil is hard to do. Growing it is easy and a simple pleasure.
To begin plant your seedlings in sunlight, fertilize it on a regular basis and then harvest the leaves. They are best when grown outdoors but they can also be grown as potted plants.
If you grow them outdoors plant them in the sunniest spot in your garden as possible. If you are growing them as potted plants make sure they are in the sunniest spot possible. In either case, you should grow at least a half dozen plants and fertilize them approximately every other week.
At some point, you will be growing more basil than you can consume. When or if this happens you can harvest your basil and then air dry them (not in the sunlight) then store them for later. Dried basil in pesto is slightly inferior to your fresh picked basil but still far superior than any pesto you can purchase at the store.
If you live in a climate where you have long sustained hard freezes, you should make cuttings, root them, pot them before the first hard freeze and keep them going through the winter. Then in the Spring set them outside in your garden. Doing it this way allows you to enjoy pesto year round, especially on long winter nights.
In any case, basil is easy to grow unless destroying houseplants is second nature to you. For some this is indeed the case.
Harvesting basil is easy. When the leaves grow to approximately 2 to 3 inches (4 to 5 centimeters) pinch them off with your fingers and lay them to the side. The aroma from the freshly pinched basil is something that cannot be described. When you have approximately 2 to 3 handfuls of FRESH basil you are close to having enough basil for two cups of fresh basil. You will need 1 cup per plate of pasta.
The next essential ingredient you need are pinyon pine nuts. You can substitute pinyon pine with cashews, peanuts or walnuts. However, doing this makes pesto begin to taste like something else. Doing so would be considered inferior to classic pesto.
To make pesto the right way you should go out and pick your own pine nuts. Where I live this is "easily" done. I say this tongue-in-cheek because picking pine nuts from the wild can often be an adventure. It can be time and labor intensive. I can go up into the Davis Mountains of far West Texas and pick the pine nuts from the Mexican pinyon pines that grow there. I don't recommend this since it is a pain in the ass. In case you still want to do this, you can use the pine seeds of just about any pinyon pine. Growing your own is not an option for obvious reasons. Pinyon pines take decades before they are big enough to produce enough seed to be of any use to you.
Not all is lost however, excellent pinyon pine nuts are easily purchased at a supermarket or specialty food store. They can also be ordered from the Internet and I have had good experiences purchasing them this way.
At the supermarket pick out the youngest, most fresh garlic you can. Old somewhat dried out garlic is bitter and not fit to consume. Don't be tempted to use it. Garlic should be firm, aromatic and have a "bite" to it. Soft garlic should be discarded.
Extra Virgin Olive Oil
If there is one ingredient that is essential but would cause flame wars on the magnitude of a super nova it is olive oil. In fact, an article on olive oil alone could be written. In the U.S., there are four grades as defined by the USDA. In Europe the grades are determined by the IOOC. Using an inferior olive oil will ruin the taste of your handcrafted pesto. Without going into the fine points of the different grades of olive oil there are, it is safe to say that you should buy the most expensive Extra Virgin Olive oil you can find.
For Americans... DO NOT USE Parmesan cheese that comes in a green can. This cannot be stressed enough as it will ruin everything. Grated, canned Parmesan cheese is terrible and smells like an athlete's jock strap after an athletic event. Do your taste buds a favor and purchase REAL Parmesan cheese from the counter where real cheese is sold. Then grate it yourself. You will be amazed at the flavor difference.
This then are the main ingredients for pesto alla genovese. You are now ready for the kitchen. Below are instructions to making the best pesto alla genovese you have ever tasted; a delight for the tongue.
Pesto Alla Genovese
Here is the pesto recipe that I use. Keep in mind that your mileage may vary.
2 cups fresh basil leaves, packed
1/4 cup grated Parmesan cheese
1/2 cup Olive oil
3 tablespoons pine nuts or walnuts
3 garlic cloves, finely minced
Place basil leaves in small batches in food processor and whip until well chopped (do about 3/4 cup at a time). Add about 1/3 the nuts and garlic, blend again.
Add about 1/3 of the Parmesan cheese; blend while slowly adding about 1/3 of the olive oil, stopping to scrape down sides of container.
Process the basil pesto until it forms a thick smooth paste. Repeat until all ingredients are used, mix all batches together well. Serve over pasta.
Basil pesto keeps in refrigerator one week, or freeze for a few months.
Contemplate over a plate of noodles topped with pesto alla genovese and enjoy.
A Special thanks to sausalito for this comment and the excellent suggestions.
Thanks also to horny smurf for his suggestion about the Parmesan cheese. I had neglected and overlooked this.