Bring a large pot of salted water to a boil. Cook orecchiette according to package instructions until al dente. Reserve 1/4 cup pasta water, then drain.

While pasta cooks, heat olive oil in a large skillet over medium heat. Add sausage and cook, breaking it up with a spoon, until browned and cooked through, about 6–8 minutes.

Add leeks and garlic to the skillet. Sauté for 4–5 minutes until leeks are soft and fragrant. Season with salt, pepper, and red pepper flakes if using.

Add cooked pasta to the skillet and toss with the sausage and leek mixture. Add reserved pasta water as needed to loosen the sauce.

Remove from heat and stir in Parmesan cheese until creamy and well combined.

Serve immediately, garnished with chopped parsley and extra Parmesan if desired.