4 cups roughly chopped arugula, kale or broccoli rabe (from 1 large bunch) 2 garlic cloves, smashed 3/4 cup almonds, roughly chopped 1/4 cup grated Parmesan cheese 1/3 cup extra-virgin olive oil, or more as needed Salt and freshly ground black pepper 2 teaspoons red-pepper flakes (optional)
In the bowl of a food processor, pulse the greens, garlic, almonds and cheese until the mixture is well combined but still coarse.
Add the olive oil and continue to pulse until the mixture is smooth. If necessary, add more olive oil 1 tablespoon at a time until the mixture is smooth but not runny.
Season the pesto with salt, pepper and red-pepper flakes, if using.
Transfer the pesto to a storage container. The pesto will keep in the refrigerator for up to a week or in the freezer for up to two months.