Boil a large pot of salted water. Cook shell pasta until al dente, then drain. Set aside and save ¼ cup of pasta water.
Heat olive oil in a large skillet over medium-high. Season steak cubes with salt and pepper. Sear in a single layer for 2–3 minutes per side until browned. Transfer to a plate.
Lower heat to medium. In the same skillet, melt butter and sauté garlic for 30 seconds. Return steak bites, toss to coat in garlic butter, and sprinkle with parsley. Remove from heat.
In a new saucepan (or cleaned skillet), melt butter over medium. Add garlic and cook 30 seconds. Stir in cream, Parmesan, salt, pepper, and Italian seasoning.
Simmer for 2–3 minutes until smooth. Add pasta and toss to coat. Use reserved pasta water if needed to loosen the sauce.
Plate the creamy Parmesan shells. Top with garlic butter steak bites, then garnish with parsley and black pepper.