Heat the oven to 425°F. Do this first. A hot oven matters more than perfect timing.
Trim the Brussels sprouts and cut them in half. Quarter the big ones. Pat them dry.
Toss the Brussels sprouts with about half the olive oil, salt, and pepper. Use your hands. Spread them out on a sheet pan, cut side down.
Put the pan in the oven and roast for about 10 minutes. This gives them a head start.
While they roast, pat the steak dry on both sides. Season well with salt and pepper. Let it sit on the counter.
Put the pan in the oven and roast for about 10 minutes. This gives them a head start.
While they roast, pat the steak dry on both sides. Season well with salt and pepper. Let it sit on the counter.
Pull the pan out. Push the Brussels sprouts to the sides to make space in the middle.
Place the steak in the center of the pan. If using garlic, scatter it around now.
Return the pan to the oven and roast for 6 to 10 minutes, depending on steak thickness and how you like it cooked.
Check the steak early. Touch it. Soft is rare, a little spring is medium rare, firm is more done.
Remove the steak from the pan and place it on a cutting board. Let it rest for about 5 minutes.
If the Brussels sprouts need more color, put the pan back in the oven while the steak rests.
Finish the steak with butter if using. Slice or leave whole.
Serve everything straight from the pan or plate it up. Eat while it is hot.