Cook your pasta according to the instruction of the box. I like to cook mine 2 minutes shy of al dente and finish in the sauce.
While the pasta in boiling away, Add the oil to your pan on medium heat. Add your onion, garlic, shallot and salt. Sauté for about 1-2 minutes.
Now, add your tomato paste and cook for another 1-2 minutes.
Next, add your vodka and stir to combine.
Add in your heavy cream and pasta water. Once the sauce starts to simmer, turn the heat down to low and add in crushed red pepper and 1/3 cup of cheese. Stir to combine.
Add your pasta to the pan and cook for another 1-2 minutes. Turn the heat off and add the spinach & butter. Fold it into the pasta. Once the spinach has shrunk, serve and top with parsley and the remaining parmigiano-reggiano (optional.) Enjoy!