Heat a large cast iron skillet over medium heat for a couple of minutes.
Add 1 tablespoon olive oil and 1 tablespoon garlic herb butter to the skillet.
Once the butter melts, add the cubed Yukon Gold potatoes and season with 1/2 teaspoon garlic powder, 1/2 teaspoon salt, and 1/2 teaspoon black pepper.
Reduce the heat to medium-low, cover the skillet, and cook the potatoes for 10 to 12 minutes, stirring occasionally, until fork-tender and golden. Lower the heat if they brown too quickly.
While the potatoes cook, season the steak bites with the remaining 1/2 teaspoon salt, 1/2 teaspoon black pepper, and 1/2 teaspoon garlic powder.
When the potatoes are cooked through, push them to one side of the pan or remove them to a plate if the skillet feels crowded.
Add the remaining 1 tablespoon olive oil and 1 tablespoon garlic herb butter to the empty side of the skillet, then increase the heat to medium-high.
Add the steak bites in a single layer and sear for 3 to 4 minutes per side, or until browned and cooked to your preferred doneness. Work in batches if needed.
Lower the heat to medium-low. Add extra garlic butter if desired, then toss the steak bites and potatoes together until glossy and evenly coated.
Taste, adjust the seasoning, garnish with parsley or thyme if using, and serve warm.
Notes
Cut the potatoes and steak into similar bite-sized pieces so they cook evenly.
Do not overcrowd the skillet when searing the steak bites. Crowding can make the steak steam instead of brown.
If cooking the steak in batches, remove the potatoes from the skillet so they do not overcook or burn.
Store leftovers in an airtight container in the refrigerator for up to 3 days.
Reheat gently in a skillet over medium-low heat for the best texture.