Bring a large pot of generously salted water to a rolling boil. Add pasta shells and cook according to package directions until al dente, usually 9-11 minutes. Before draining, reserve 1 cup of pasta water. Drain shells and set aside without rinsing.

While pasta cooks, heat butter and olive oil together in a large skillet over medium heat. Once butter melts and foams, add finely chopped onion. Cook for 3-4 minutes, stirring occasionally, until onion softens and turns translucent. Add minced garlic and cook for 1 minute until fragrant.

Increase heat to medium-high and let pan get hot for 30 seconds. Pat steak pieces dry with paper towels, then season generously with salt, black pepper, and 1½ teaspoons smoked paprika. Add seasoned steak to hot skillet in a single layer, working in batches if needed. Sear for 2-3 minutes without moving, until golden crust forms. Flip and sear other side for 2 minutes. Steak should be browned outside but slightly pink inside. Transfer to a plate.

Reduce heat to medium. Pour heavy cream into the same skillet and use a wooden spoon to scrape up browned bits from the bottom. Whisk in additional ½-1 teaspoon smoked paprika. Let cream simmer gently for 3-4 minutes, stirring occasionally, until it thickens slightly and coats the back of a spoon.

Add grated Parmesan cheese and whisk until it melts completely into the sauce. Taste and adjust seasoning with salt and pepper.

Return seared steak and any accumulated juices to the skillet. Add drained pasta shells and toss everything together gently but thoroughly until every shell and piece of steak is coated with sauce. If sauce is too thick, add reserved pasta water a tablespoon at a time until reaching perfect consistency.

Remove from heat and sprinkle fresh chopped parsley over the top. Toss once more. Serve immediately on warm plates, topped with extra Parmesan cheese if desired.