As seen here on foodnetwork.com
2 cups packed fresh basil leaves
2 cloves garlic
1/4 cup pine nuts
2/3 cup extra-virgin olive oil, divided
Kosher salt and freshly ground black pepper, to taste
1/2 cup freshly grated Pecorino cheese (see Cook's Note)
Combine the basil, garlic, and pine nuts in a food processor and pulse until coarsely chopped. Add 1/2 cup of the oil and process until fully incorporated and smooth. Season with salt and pepper.
If using immediately, add all the remaining oil and pulse until smooth. Transfer the pesto to a large serving bowl and mix in the cheese.
If freezing, transfer to an air-tight container and drizzle remaining oil over the top. Freeze for up to 3 months. Thaw and stir in cheese.
** I didn't use it immediately OR freeze it and it's still tasting fresh. It's been in my fridge for a few weeks and didn't even get dark and discolored or anything like that.