Remove the sirloin steak from the refrigerator 20 minutes before cooking to bring it to room temperature and pat it thoroughly dry with paper towels.
Season both sides of the steak evenly with the sea salt and black pepper, pressing the seasoning into the meat.
Heat the avocado oil in a heavy cast-iron skillet over medium-high heat until it begins to shimmer and slightly smoke.
Carefully place the steak in the hot skillet and sear for 3 to 4 minutes without moving it until a deep, golden-brown crust has formed.
Flip the steak and immediately add the grass-fed butter, garlic cloves, rosemary, and thyme to the pan.
Tilt the skillet slightly so the melting butter pools with the herbs and garlic, then use a large spoon to continuously baste the top of the steak for 2 to 3 minutes.
Remove the steak from the skillet and place it on a cutting board to rest for at least 5 to 7 minutes to allow the juices to redistribute.
While the steak rests, add the asparagus spears to the same skillet and sauté in the remaining herb butter for 4 to 5 minutes until tender and lightly charred.
Slice the steak against the grain and serve alongside the buttery asparagus, drizzling any remaining pan juices over the top.