Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the sweet potato and cut into 1-inch cubes, then toss them on the baking sheet with half of the ghee and a pinch of sea salt.
Roast the sweet potatoes for 20 minutes.
While potatoes roast, trim the woody ends off the asparagus; after the 20 minutes are up, add the asparagus to the baking sheet and roast everything for another 10-12 minutes.
Pat the sirloin steak dry with paper towels and season both sides generously with sea salt and cracked black pepper.
Heat a cast-iron skillet over medium-high heat and add the remaining ghee.
Place the steak in the hot skillet and sear for 4-5 minutes per side for medium-rare.
During the last 2 minutes of cooking, add the smashed garlic cloves and rosemary sprig to the pan.
Tilt the skillet and use a spoon to continuously baste the steak with the hot, aromatic garlic-herb ghee.
Remove the steak from the pan and let it rest for 5 minutes before slicing against the grain and serving with the roasted vegetables.