Cook the rigatoni according to package directions in a large pot of salted boiling water until al dente. Reserve about 1 cup of the pasta water before draining.

While the pasta cooks, heat the olive oil in a large skillet or Dutch oven over medium heat. Add the sliced leeks and cook, stirring occasionally, until softened, about 5-7 minutes.

Add the chopped garlic scapes and minced garlic to the skillet. Cook for another 2-3 minutes until fragrant and slightly tender. Stir in the red pepper flakes, if using.

Pour in the heavy cream and vegetable broth. Bring to a gentle simmer, then reduce heat to low. Stir in the grated Parmesan cheese until the sauce is smooth and slightly thickened.

Add the drained rigatoni to the skillet with the sauce. Toss to coat evenly. If the sauce seems too thick, add a splash of the reserved pasta water until it reaches your desired consistency.

Season generously with kosher salt and freshly ground black pepper to taste. Serve immediately, garnished with fresh chopped parsley and extra grated Parmesan cheese.