Heat 1 tbsp olive oil in a large cast iron skillet over medium-high heat.
Cook halved potatoes cut-side down for 5 to 6 minutes until golden. Flip and cook 4 to 5 more minutes until tender. Remove and set aside.
Pat steak cubes completely dry. Season with salt, pepper, garlic powder, and rosemary.
Add remaining olive oil to the skillet and increase heat to high.
Sear steak bites in a single layer for 1 to 2 minutes per side without moving. Work in batches if needed.
Reduce heat to medium. Add butter and minced garlic. Toss steak in garlic butter for 30 seconds.
Return potatoes to the pan. Toss together and cook 1 final minute. Garnish with parsley and serve.