Start by cutting the sirloin steak into 2-inch cubes. This size sears well and stays juicy. Sprinkle salt and pepper generously over the pieces, then let them rest for about 10 minutes at room temp. That resting time helps the meat cook evenly and keeps it tender.
Heat your skillet over medium-high heat and melt the butter until it’s foamy. Add the steak pieces in a single layer without crowding the pan. Let them sear for about 3 minutes undisturbed to form a crust. Then flip and cook for another 2–3 minutes. Remove the steak bites from the skillet and set them aside.
Lower the heat and add your minced garlic right into the same skillet. Let it sizzle for 30 seconds to a minute—don’t let it brown too much. Use your spoon to scrape up all those brown bits from the bottom. They carry all the flavor from the steak. Add the cooked steak bites back into the skillet and toss them in the garlic butter to coat.
In the same skillet (yes, keep using those flavorful drippings), pour in the beef broth and bring it to a low simmer. Whisk to lift up the browned bits, then slowly stir in the heavy cream. Let the mixture simmer for 2–3 minutes until it starts to thicken. Now stir in the Parmesan cheese, whisking until smooth and creamy. If you like a bit of heat or smokiness, add your red pepper flakes or paprika now.
Return the steak bites to the skillet one last time, letting them soak up that creamy Parmesan sauce. Toss gently until everything is coated evenly. Sprinkle chopped parsley on top, and that’s it—you’re ready to eat!