Bring a large pot of generously salted water to a boil. Cook rigatoni according to package directions until al dente, about 10-12 minutes. Reserve 1/2 cup pasta water before draining. Drain pasta but do not rinse.

While pasta cooks, pat beef strips dry with paper towels. Season both sides with salt, pepper, and paprika. Heat olive oil in a large skillet over high heat until shimmering. Working in batches to avoid crowding, sear beef strips for 1-2 minutes per side until browned but still slightly pink in center. Transfer to a plate and set aside.

Reduce heat to medium and melt butter in the same skillet. Add diced onion and cook for 3-4 minutes until soft and translucent. Add minced garlic and tomato paste, stirring constantly for 1 minute until fragrant and paste darkens slightly.

Pour in beef broth, scraping the bottom of the pan to release browned bits. Let bubble for 30 seconds, then add heavy cream and dried oregano. Stir to combine and bring to a gentle simmer. Cook for 3-5 minutes, stirring occasionally, until sauce thickens enough to coat the back of a spoon.

Reduce heat to low. Add freshly grated Parmesan cheese a handful at a time, stirring constantly until each addition melts smoothly. The sauce should be smooth, creamy, and glossy.

Add drained rigatoni and seared beef (with any accumulated juices) to the skillet. Toss everything together gently until pasta and beef are thoroughly coated with sauce. If sauce is too thick, add reserved pasta water one tablespoon at a time until desired consistency is reached.

Taste and adjust seasoning with additional salt and pepper if needed. Garnish with chopped fresh basil or parsley and extra Parmesan. Serve immediately.