Combine everything in a blender or food processor and blend until smooth.
Add more or less olive oil to reach the desired consistency.
Store the rosemary pesto in a jar in the refrigerator for up to 5 days.
Notes
To make a dairy-free or vegan rosemary pesto recipe, you can replace the parmesan with nutritional yeast. Star with a couple tablespoons of nutritional yeast and then add more to taste.