Spaghetti with garlic olive oil and anchovies was almost a weekly dinner growing up especially on meatless Fridays or after a night of bar hopping. Pop's rendition is a little soupier than traditional. That's why he called it anchovy soup.
Put the spaghetti in a large pot of well-salted rapidly boiling water and cook only until firmly al dente.
While the pasta is cooking, warm the olive oil in a small skillet over medium heat. Add the garlic and capers and cook for about 1 minute, without letting it brown. Stir in the anchovies and red pepper, melting the anchovies, then turn off the heat.
Reserve 1 cup of starchy pasta water, drain the pasta and return it to the pot. Pour in the garlic mixture, add the parsley, if using, and toss well to coat. Add the pasta water a little at a time to achieve desired consistency and finish cooking the pasta. Serve with grated Parmesan or Pecorino if desired.