Preheat the oven to 350ºF (180ºC) and line a baking sheet with parchment paper. Scatter the almonds on the sheet and toast for 8 to 10 minutes, stirring halfway through. The almonds should be fragrant and golden. Set aside to cool slightly.
While the almonds are toasting, wash and dry the spinach and arugula. Use a salad spinner if you have one to ensure the leaves are dry.
Place the spinach, arugula, toasted almonds, Parmesan cheese, salt, and garlic in the bowl of a food processor. Pulse 5 to 10 times, or until the mixture is coarse and chunky.
With the food processor running, drizzle the olive oil in a slow, steady stream. Stop to scrape down the sides of the bowl a couple of times as needed. Once the oil is incorporated, process for 5 to 10 seconds or until the pesto reaches your desired texture. Taste and adjust seasoning if necessary.
Spoon the pesto into a clean glass jar. Store, tightly covered, in the fridge for up to 2 weeks or in the freezer for up to 2 months.
Notes
Store the pesto in clean glass jars with tight fitting lids in the refrigerator.
Spinach pesto will keep in the freezer for up to two months.