Bring a large pot of salted water to a boil. Add the pasta shells and cook according to package directions until al dente, about 8-10 minutes. Drain and set aside, reserving 1/2 cup of pasta water.

While the pasta cooks, heat 2 tbsp olive oil in a large skillet over medium-high heat. Season the sliced steak with salt, black pepper, and half the Italian seasoning. Sear the steak for 2-3 minutes per side until browned and cooked to your desired doneness. Remove from the skillet and set aside.

In the same skillet, reduce heat to medium and add 2 tbsp butter. Once melted, add minced garlic and sauté for 1-2 minutes until fragrant.

Pour in the heavy cream and milk, stirring to combine. Bring to a gentle simmer, then gradually whisk in the Parmesan cheese until the sauce is smooth and thickened, about 3-4 minutes. If too thick, add reserved pasta water.

Add the cooked pasta shells to the sauce, tossing to coat evenly. Let it simmer for 1 minute.

Return the seared steak to the skillet, along with any juices. Toss gently over low heat for 1-2 minutes.

Remove from heat and stir in the remaining 2 tbsp butter. Garnish with chopped parsley.

Serve immediately with extra Parmesan if desired.