Preheat your oven to 400°F (200°C).
Halve the baby potatoes and toss them on a baking sheet with the olive oil, garlic powder, and a pinch of sea salt.
Roast the potatoes for 20 minutes, flipping halfway through.
While potatoes roast, remove the steak from the refrigerator and let it sit at room temperature for 20 minutes. Pat it completely dry with paper towels and season all sides with sea salt and black pepper.
Heat a cast-iron skillet over medium-high heat until very hot. Place the steak in the pan and sear for 3-4 minutes per side for medium-rare.
During the last 2 minutes of searing, add the ghee, smashed garlic clove, and rosemary sprig to the pan. Tilt the pan slightly and use a spoon to continuously baste the steak with the melted garlic ghee.
Remove the steak from the pan and transfer to a cutting board. Let it rest for at least 5-10 minutes to allow the juices to redistribute.
Add the asparagus spears to the baking sheet with the potatoes and roast for an additional 8 minutes until the vegetables are tender-crisp and golden.
Serve the rested filet mignon alongside the roasted potatoes and asparagus.