Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Place the broccoli florets on the baking sheet, drizzle with half of the melted ghee, and sprinkle with a pinch of sea salt and black pepper.
Roast the broccoli for 15 to 20 minutes, tossing halfway through, until the edges are golden and tender.
While the broccoli roasts, pat the sirloin steak dry with a paper towel and season both sides generously with sea salt, black pepper, and dried thyme.
Heat a cast-iron skillet over medium-high heat and add the remaining ghee.
Once the skillet is shimmering, add the steak and sear for 3 to 4 minutes per side for medium-rare.
During the last 2 minutes of cooking, add the smashed garlic cloves to the pan and spoon the hot garlic-infused ghee over the steak repeatedly.
Remove the steak from the pan and let it rest on a cutting board for 5 minutes before slicing against the grain.
Serve the sliced steak alongside the roasted broccoli, drizzling any remaining pan juices over the meat.