Bring a large pot of water up to a rolling boil.

While the water heats, start cooking the sausage. Break it up in a large skillet over medium-high heat. You can use a wooden spoon or spatula, but I find a potato masher works best.

Add the garlic cloves and chili flakes (if using), then cook until the sausage is nicely browned.

When the water is boiling, season generously with salt then add the broccoli rabe. Cook until al dente, about 2 minutes, then use a spider or handheld strainer to remove it from the water.

Drain the broccoli rabe well, then add it to the pan with the sausage and stir to combine. Let simmer over very low heat.

Add the pasta to the water (make sure it's still at a rolling boil), stir, then cook according to package directions until just shy of al dente (it will continue cooking in the pan).

Reserve a cup or two of pasta cooking water, then drain and immediately add the pasta to the pan with the sausage and broccoli rabe.

Turn up the heat to medium-high and toss until well combined. Add pasta water a few splashes at a time and continue tossing until the sauce thickens up a bit.

Turn off the heat, then add the parmesan cheese and parsley, then toss vigorously until incorporated.

Spoon pasta into bowls, then drizzle each with a bit of olive oil and sprinkle with parsley and more parmesan cheese. Serve immediately.