Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package directions until just shy of al dente. Reserve ½ cup (120 ml) of the pasta cooking water, then drain the pasta and set aside.
12 oz (340 g) dry rigatoni pasta, ½ cup (120 ml) reserved pasta water
Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for 4 to 5 minutes, stirring occasionally, until softened and lightly translucent.
2 tbsps (15 ml) olive oil, ½ cup (75 g) diced yellow onion
Add the minced garlic and cook for 30 seconds, stirring constantly, until fragrant.
4 cloves (12 g) garlic
Stir in the chopped Calabrian chilis and tomato paste and cook for about 1 minute, stirring frequently, until the tomato paste darkens slightly and becomes aromatic.
¼ cup (60 g) chopped Calabrian chilis, 2 tbsps (32 g) tomato paste
Pour in the fire-roasted tomatoes and stir to combine. Bring the mixture to a gentle simmer and cook for 3 to 4 minutes to allow the flavors to develop.
1 can (14.5 oz / 411 g) diced fire-roasted tomatoes
Reduce the heat to medium-low and stir in the heavy cream. Simmer gently for 2 to 3 minutes, stirring occasionally, until the sauce is smooth and lightly thickened.
1 cup (240 ml) heavy cream
Remove the skillet from the heat and add the grated Parmesan cheese. Stir continuously until the cheese melts completely into the sauce and the mixture becomes creamy.
¾ cup (75 g) Parmesan cheese
Season with black pepper and kosher salt to taste. Stir in the lemon juice if using.
1 tsp (3 g) freshly ground black pepper, 1 tsp (6 g) kosher salt, 1 tbsp (15 ml) fresh lemon juice
Add the drained rigatoni to the skillet and toss to coat the pasta evenly in the sauce. Add reserved pasta water a little at a time while tossing until the sauce loosens slightly and clings to the pasta.
Serve immediately, topped with additional Parmesan cheese and chopped parsley if desired.
2 tbsps (8 g) chopped parsley