01 - Pat steak cubes dry with paper towels and season evenly with salt and pepper.
02 - Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add mushrooms and cook for 4 to 5 minutes, stirring occasionally, until browned and tender. Remove mushrooms and set aside.
03 - Add 1 tbsp olive oil and 1 tbsp butter to the same skillet. When hot, add steak bites in a single layer, cooking in batches if necessary to avoid overcrowding. Sear without stirring for 2 to 3 minutes, then flip and cook an additional 2 minutes until browned and cooked to desired doneness.
04 - Stir in remaining butter and garlic. Cook for 1 minute until fragrant.
05 - Return mushrooms to skillet. Add parsley, thyme, and chili flakes if using. Toss to coat everything evenly with garlic butter.
06 - Serve immediately, garnished with additional parsley if desired.