Crisp the potatoes: Par-cook potato halves in a covered microwave bowl with 2 tablespoons of water for 4 minutes until fork-tender, then drain and pat thoroughly dry. Heat 1 tbsp olive oil and 1 tbsp butter in a 12-inch cast-iron skillet over medium-high heat. Add potatoes cut-side down and fry for 5 minutes undisturbed until deeply golden and crispy. Transfer potatoes to a plate.

Season and sear the steak: Pat steak cubes dry with paper towels and toss with 1 tbsp olive oil, garlic powder, smoked paprika, kosher salt, and black pepper. Turn heat to high until the skillet is smoking hot. Working in two uncrowded batches, sear steak bites for 3 to 4 minutes total, turning once or twice to form a deeply browned crust while keeping the interior juicy medium (135°F / 57°C). Transfer steak to plate with potatoes.

Melt garlic herb butter: Reduce skillet heat to medium-low. Add the remaining 3 tablespoons of butter. Once foaming, add minced garlic, fresh rosemary, and fresh thyme. Cook for 60 seconds until intensely aromatic, scraping up any delicious browned steak bits from the pan.

Toss and glaze: Return the seared steak bites and crispy potatoes to the skillet. Toss rapidly for 1 to 2 minutes until everything is bubbling hot and drenched in glossy garlic herb butter.

Garnish and serve: Remove from heat immediately to avoid overcooking the steak. Shower with freshly chopped parsley and serve piping hot straight from the cast-iron skillet.