Bring a large pot of salted water to a rolling boil. Add pasta shells and cook until al dente, approximately 8 to 10 minutes. Reserve 0.25 cup of pasta water before draining.

Pat steak cubes dry with paper towels to ensure optimal Maillard reaction. Season thoroughly with salt, black pepper, and garlic powder.

Heat olive oil in a large cast-iron skillet over high heat until it reaches the smoke point.

Place steak cubes in the skillet in a single layer, ensuring no overcrowding. Sear for 2 minutes undisturbed, then turn and cook for an additional 2 minutes until an internal temperature of 135°F (57°C) is reached for medium-rare.

Reduce heat to medium. Add 2 tablespoons of butter and 2 cloves of minced garlic to the skillet. Baste the steak for 60 seconds. Remove steak and any residual butter from the pan; set aside to rest.

Deglaze the skillet or use a clean saucepan over medium heat. Melt the remaining 2 tablespoons of butter and sauté the remaining 3 cloves of minced garlic for 30 seconds.

Pour in the heavy cream and bring to a gentle simmer. Reduce heat to low and whisk in the Parmesan cheese gradually until a homogenous, thickened emulsion forms.

Integrate the cooked pasta shells into the cream sauce. If the viscosity is too high, add the reserved pasta water in 1-tablespoon increments until the desired consistency is achieved.

Incorporate the rested steak bites and accumulated juices into the pasta or plate them directly on top.

Garnish with chopped Italian parsley and serve immediately.