Preheat your oven to 425°F.
Pat the flank steak dry with paper towels and season generously with salt, pepper, garlic powder, and dried rosemary on both sides.
In a small bowl, combine the olive oil with a pinch of salt and pepper to make a marinade.
Brush the steak with the olive oil marinade and let it rest at room temperature for about 10 minutes.
Meanwhile, wash the mini potatoes and cut any larger ones in halves to ensure even roasting.
Toss the mini potatoes in a bit of olive oil, salt, pepper, and a sprinkle of garlic powder.
Place the potatoes on a baking sheet in a single layer and roast in the preheated oven for 20-25 minutes or until golden and crispy, flipping halfway through.
While the potatoes roast, heat a cast iron or oven-safe skillet over medium-high heat.
Sear the flank steak for about 3-4 minutes on each side until a nice crust forms.
Transfer the skillet with the steak into the oven (if your skillet is oven-safe) and roast for an additional 5-7 minutes for medium-rare, or until desired doneness is reached.
Remove the steak from the oven and let it rest for 5 minutes before slicing against the grain.
Serve the sliced steak alongside the crispy roasted mini potatoes for a hearty, balanced meal.