Preheat your oven to 400°F (200°C).
Halve the baby potatoes and toss them on a baking sheet with the olive oil and a pinch of the sea salt and black pepper.
Roast the potatoes for 20-25 minutes, flipping halfway through, until they are golden brown and tender.
Pat the sirloin steak dry with paper towels and season both sides generously with the remaining sea salt and black pepper.
Heat a cast-iron skillet over medium-high heat until it is very hot and slightly smoking.
Place the steak in the skillet and sear for 3-4 minutes per side for medium-rare, or until your desired level of doneness is reached.
Reduce the heat to medium and add the ghee, smashed garlic cloves, and the rosemary sprig to the pan.
Tilt the skillet and use a large spoon to continuously baste the steak with the foaming garlic ghee for about 1-2 minutes.
Transfer the steak to a cutting board and let it rest for at least 5-8 minutes before slicing.
In the same skillet, add the asparagus and sauté in the remaining garlic ghee for 3-5 minutes until bright green and crisp-tender.
Slice the steak against the grain and serve alongside the roasted potatoes and sautéed asparagus.