Back when I was a wee food labber who spent his summers at band camp,* my favorite day of the summer was when the camp's cook, Glen, would make his pesto. We'd have a camp-wide pesto spaghetti eating contest, in which I may have been the only competitor. This simultaneously made me a winner and a complete loser each time.
*Ok, chamber music camp. But really the same sort of hormonal, nerdy crew.
What can I say? I loved my pesto back then as much as I love it now. Today, we're gonna stick it on pizza. But first, a few words to the wise.
When we talk pesto here, we're talking the genovese variety made with basil, pine nuts, and cheese that we're most familiar with. There are, of course, other varieties of pesto kicking around, but we're not gonna bother with them for now.
The easiest way to make genovese pesto is in the food processor**; just throw in your ingredients (that's basil, pine nuts, parmesan cheese, garlic, and olive oil), buzz it up, and you're good to go. But there are ways to improve it.
**You mortar and pestle purists can balk all you want. Meanwhile, I'll be enjoying my pesto while I wait for you to finish yours.
For one thing, pesto made in this way has a tendency to lose its color, turning from a rich, deep green to a drab olive green, especially if you let it sit in the fridge for a night or two. How do you prevent this from happening? Blanch the basil.
See, puréed basil leaves lose their color as air and natural enzymes interact with pigments in the leaves. Blanching the leaves by dunking them in boiling water for just a few moments (about 15 to 30 seconds) will deactivate those pesky enzymes, helping your pesto to stay deep, bright green, even after days of storage and cooking.
I also like to add some spinach to the mix, to add some more green without overwhelming the other flavors with excess basil.
As for application, you can't just use the exact same pesto you'd use on pasta, throw it on a pizza, and expect it to work. The problem is the oil. In a dish of pasta, the excess olive oil combines with the pasta water to form a sauce. On a pizza, all it does is pool into greasy slicks on the surface of the pizza.
You have two options. If you want to make an all-purpose pesto, you can make it as normal*** and then blot out some of the excess oil before adding the pesto to your pizza. Alternatively, just make it with a bit less oil to begin with. My recipe is made with equal parts (by weight) basil, spinach, parmesan, and pine nuts, with a single garlic clove (also added to the blanching water as the spinach and basil cook, to take away some of its sharpest edges) and 1/3 cup of olive oil.
***in the recipe linked, increase the oil from 1/3 cup to 1/2 cup
A teaspoon of lemon zest adds some brightness and balances the whole thing out.
When it comes to application and other toppings, I like to keep things sparse. Some folks like to spread the pesto around like a tomato sauce. I prefer applying in discrete spots to create some points of interest as you work your way through the pie.
Speaking of cheese, I'm going with a three-part mix. A bottom later of grated parmesan, followed by fresh mozzarella (di bufala if you're wearing your fancy pants), and dollops of ricotta. As the pie bakes, the mozzarella spreads out into a milky blanket, while the dollops of ricotta soften and the pesto spreads, touching and mingling with the ricotta in a way that would be considered inappropriate in some, more restrictive, societies.
If you're feeling extra feisty, you can always add more toppings if you desire. Pesto is a pretty strongly flavored sauce to begin with, and according to The Pizza Snob's Approach to Toppings, every topping must be more flavorful than the one that came before it. Thus for topping a pesto pie, you'd need to go with bold flavors like sun-dried tomatoes, anchovies, capers, and olives.
At least, that's what I'd do. Feel free to do whatever the heck you'd like. It's your pizza; nobody's stopping you.