To the bowl of a food processor, add the basil, pepitas, and garlic. Process until finely chopped.
Add the parmesan and lemon juice and blend to combine. Drizzle in the oil with the processor running and blend until smooth. Season to taste with salt and pepper.
Store in an airtight container in the refrigerator for up to one week. (Note 2)
Pasta and mushrooms
With a damp paper towel, brush any dirt off the mushrooms. (Note 3)
Heat a large skillet over medium heat. Add the butter. When melted, add the mushrooms, and cook for 7-8 minutes until brown. The mushrooms will slowly release their moisture. Once the liquid evaporates, the mushroom will start to brown.
Meanwhile, cook the pasta in well-salted water until al dente. Before draining, reserve ½ cup of pasta water.
Add the drained pasta to the browned mushrooms. Turn off the heat and stir in the pesto. Add enough pasta water - starting with ¼ cup - to bring together the sauce.
Garnish with pepitas and Parmesan cheese. Serve immediately.
Substitute pepitas with walnuts, almonds, pistachios, pecans, macadamia nuts, or pine nuts. Choose what you love or have readily available.
Save extra pesto to use in other recipes.
Mushrooms should not be held under running water or immersed in water to clean. They will absorb too much water and become soggy.