Prepare the Steak
1. Remove the sirloin from the refrigerator and pat it completely dry with paper towels. Cut the steak into bite-sized cubes, about 1.5 inches, discarding any excess fat or gristle as you work.
2. Place a large cast iron or stainless steel skillet over medium-high heat and let it warm for 2 to 3 minutes until it's very hot. A properly heated skillet ensures a beautiful golden crust on each bite.
Sear and Finish
3. Add the olive oil to the hot skillet, then carefully place the steak bites in a single layer without crowding. Let them cook undisturbed for 3 to 4 minutes until they develop a golden crust, then flip and cook for another 2 to 3 minutes for medium-rare doneness.
4. Reduce the heat to medium, then add the butter and chopped garlic to the skillet, stirring gently to coat all the steak bites. Cook for 1 to 2 minutes until the garlic becomes fragrant and the butter turns a light golden color.
5. Remove the skillet from heat, then taste a piece and season with salt and pepper to your preference. Toss the steak bites one final time to ensure they're evenly coated in the garlic butter sauce, then serve immediately.