Bring a large pot of heavily salted water to a boil. Cook rigatoni according to package instructions until al dente. Drain, reserving 1/2 cup of the pasta cooking water.

Pat the steak cubes dry with paper towels and season thoroughly with salt and black pepper.

In a large cast-iron skillet, melt 2 tablespoons of butter over medium-high heat until foaming. Add steak cubes in a single layer, searing for 2-3 minutes per side until a brown crust forms.

Reduce the heat to medium. Add the remaining 2 tablespoons of butter and minced garlic to the skillet. Baste the steak with the melting garlic butter for 60 seconds, then remove steak and all pan juices to a plate and cover loosely with foil.

Wipe the skillet briefly if needed, then pour in the heavy cream. Bring to a gentle simmer over medium heat, scraping up any browned bits (fond) from the bottom of the pan.

Reduce heat to low. Gradually whisk in the Parmesan, Mozzarella, Fontina, and Provolone cheeses one handful at a time, whisking constantly until the sauce is smooth and the cheese is fully melted.

Whisk in the ground nutmeg. If the sauce is too thick, add the reserved pasta water 1 tablespoon at a time until the desired consistency is achieved.

Add the cooked rigatoni to the cheese sauce and toss until every noodle is evenly coated.

Divide the pasta into bowls, top with the garlic butter steak bites, and garnish with chopped fresh parsley before serving.