In a large sauce pot, bring generously salted water to a rolling boil.
Place a large sauté pan over medium-low heat (I recommend a flat-sided pan for this recipe), then add the olive oil. Add the garlic, anchovies, and pepper flakes, coat with the oil, and cook slowly, stirring occasionally with a heat-resistant spatula or wooden spoon, until the garlic is fragrant and the anchovies are melting into the oil, 5-7 minutes. Keep an eye on the pan to make sure the garlic doesn't burn or toast; adjust the heat if necessary.
Meanwhile, once the pasta water reaches a boil, add the spaghetti and cook according to package instructions until al dente. Just before it's finished, add the parsley to the sauté pan and toss with the other ingredients.
Use tongs to carefully transfer the pasta directly from the boiling water to the sauté pan (you want some pasta water to transfer; it will help create the sauce).
Increase the heat to medium and toss the pasta with the pan ingredients. If needed, add a small drizzle each of oil and pasta water to keep everything smooth. Taste the pasta and season with salt to taste.
Transfer to individual serving plates or bowls and top with grated Parmigiano-Reggiano.
Notes
1/2 teaspoon crushed red pepper won't add much heat, just a bit of flavor and warmth in the background. I added an extra pinch of crushed red pepper, which still didn't overpower. You can add a bit more if you like a kick.Barely adapted from Appetites by Anthony Bourdain