Prepare the cream sauce. In a high speed blender, blend 1 cup of broth, the soaked cashews and tomato paste, until smooth and creamy. Set aside.
Warm olive oil in a dutch oven or large sauce pan over medium heat. Sauté the diced onion until starting to soften, then add the minced garlic and continue to sauté another minute until fragrant.
Add 3 cups of broth, the penne, roasted red peppers, nutritional yeast, sea salt, oregano and red pepper flakes and stir until ingredients are evenly distributed. Cover and bring to a strong simmer, then turn heat down to medium-low. Continue to simmer covered, stirring occasionally, for about 15 minutes (up to 20 if you like a softer texture). You want the pasta to be mostly cooked before adding the cream sauce.
Once the pasta has almost cooked to your desired texture, uncover and add the cream sauce. Stir until the noodles are evenly coated, then stir in the spinach. Cover again for a few minutes to let the spinach wilt, warm the cream sauce and finish cooking the noodles. Stir in a splash more broth as needed if the sauce is getting too dry for your liking.
Season with additional salt, to taste. Serve immediately with fresh basil garnish. Store any leftovers in a sealed container in the refrigerator and eat within 4 days.
You can also soak the cashews in boiled water for 20 minutes to save time. If soaking overnight, place in the refrigerator.
Be sure to stir occasionally while simmering, to prevent noodles from sticking to the bottom of the pan.
If you find it’s getting too try, add more broth during simmering or after you add the cream sauce. I usually end up adding about 1/2 cup or so after warming the cream sauce.
Adding the cashew cream at the end prevents the sauce from burning to the bottom of the pan.