Prepare the steak: Cut the steak into bite-sized pieces. Pat them thoroughly dry with paper towels, then season generously with salt and black pepper.
Heat the skillet: Place a heavy-bottomed skillet, preferably cast iron, over high heat. Add the olive oil and heat until shimmering.
Sear the steak: Add the steak pieces in a single layer. Cook for 1–2 minutes per side, or until deeply golden on the outside. Work in batches if necessary to prevent overcrowding.
Add garlic butter: Reduce the heat to medium. Add the butter and minced garlic, then toss the steak bites until coated and fragrant.
Rest the steak: Transfer the steak to a clean plate and let it rest while you prepare the sauce.
Make the sauce: Using the same skillet, melt the butter over medium heat. Add the minced garlic and sauté for about 30 seconds.
Add the cream: Slowly pour in the heavy cream while stirring. Allow it to gently warm without bringing it to a rapid boil.
Add Parmesan: Whisk in the grated Parmesan until melted and smooth. If needed, add a small splash of milk to loosen the sauce.
Season: Add salt, black pepper, and a small pinch of nutmeg if desired.
Combine: Return the steak bites to the skillet and gently toss them through the sauce.
Finish: Simmer for 1–2 minutes, just until the steak is warmed through and coated in the creamy sauce. Serve immediately.