Begin by boiling a pot of salted water for the rigatoni. Cook the rigatoni according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.

While the pasta is cooking, season both sides of the ribeye steaks with salt and black pepper.

Heat a large skillet over medium-high heat and add 2 tablespoons of the butter. Once melted and sizzling, add the steaks to the skillet. Cook for 4-5 minutes on each side for medium-rare, or until your desired doneness is reached.

During the last minute of cooking the steaks, add the minced garlic and remaining butter to the skillet. Spoon the melted garlic butter over the steaks while they finish cooking. Remove the steaks from the skillet and let them rest.

In the same skillet, add olive oil and diced onion. Sauté for 3-4 minutes until the onion is translucent. Add minced garlic and cook for an additional 1-2 minutes until fragrant.

Pour in the heavy cream, stirring to combine, and let it simmer for 2-3 minutes. Gradually whisk in the grated Parmesan cheese until the sauce is smooth and creamy.

Add the cooked rigatoni to the skillet, tossing well to combine with the sauce. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached. Season with salt and pepper to taste.

Slice the garlic butter steak and serve on a plate with a generous portion of creamy Parmesan rigatoni. Garnish with chopped parsley.