Begin with bringing a large pot of water to boil for the pasta.
In a large skillet, heat olive oil and add pancetta until browned. Add in anchovies and cook until dissolved, about 1 minute. Add butter, garlic and pepper flakes. Cook for 30 seconds or until fragrant. Add in spinach, salt and black pepper and cook until wilted, about 2 to 3 minutes. Remove from heat.
Once the water is boiling, salt and oil the water. Stir. Add spaghetti and cook according to package instructions until al dente. Reserve 1 cup pasta water. Drain pasta. Toss pasta and spinach mixture in a large bowl. Add in pasta water, as needed, if dry. Top with parmesan and parsley.
Notes
Don't be tempted to skip the anchovies. If you feel like you won't like them, you probably have never tried them. Worcestershire sauce gets its flavor from anchovies. TRUST.While the water is coming to a boil, prep the other ingredients in small bowls so as this comes together quickly, everything will be ready to go. In France, they call this "mise en place". It means "everything in its place". It helps tremendously to do the prep and have ingredients ready to roll. This is one of those recipes that I feel this is important.To have this much garlic chopped quickly, I recommend using a garlic press. It's super fast and easy to just squeeze the cloves through. I've gone through many over the years. The one I use now has lasted by far the longest and worked best. Click here to find the one I've got.