Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the cubed sweet potato and broccoli florets with avocado oil, half of the sea salt, and half of the black pepper.
Spread the vegetables in a single layer on the baking sheet and roast for 20 minutes until the potatoes are tender and the broccoli is slightly caramelized.
While the vegetables roast, pat the sirloin steak completely dry with paper towels and season both sides with the remaining salt and pepper.
Heat a cast-iron skillet over medium-high heat until very hot, then place the steak in the pan to sear for 3-4 minutes per side for medium-rare.
Reduce the heat to low and add the ghee, minced garlic, and chopped rosemary to the skillet.
Tilt the pan slightly and use a spoon to continuously baste the steak with the melting garlic-herb butter for 1 minute.
Remove the steak from the pan and let it rest for 5 minutes before slicing it against the grain and serving alongside the roasted vegetables.