Bring a large pot of salted water to a boil. Cook shell pasta until al dente according to package directions, about 8 to 10 minutes. Reserve 1/2 cup of pasta water before draining. Set pasta aside.

Pat steak pieces completely dry with paper towels. Season generously with salt and black pepper on all sides.

Heat olive oil in a large skillet over medium-high heat until shimmering. Sear steak bites in a single layer for 2 to 3 minutes per side until a deep brown crust forms. Work in batches if needed. Transfer to a plate and tent loosely with foil.

Reduce heat to medium. Add butter to the same skillet. Once melted, stir in minced garlic and cook for about 1 minute until fragrant. Do not let the garlic brown.

Pour in the heavy cream and stir to combine. Bring to a gentle simmer, then gradually whisk in Parmesan cheese until smooth and creamy. Season with salt and pepper. Add reserved pasta water one splash at a time if the sauce is too thick.

Add the cooked shell pasta and toss gently to coat. Simmer together for 1 to 2 minutes so the pasta absorbs the flavors.

Divide pasta into serving bowls. Arrange steak bites on top and drizzle over any resting juices from the plate. Garnish with fresh parsley if using. Serve hot immediately.