Remove the 20 oz bone-in rib steak from the refrigerator 45–60 minutes before cooking. Pat dry thoroughly with paper towels to remove surface moisture—this helps form a good crust.

Season

Just before cooking, season both sides generously with kosher salt (about 2 tsp total) and freshly ground black pepper (about 1 tsp). Press the seasoning gently into the meat.

Preheat pan

Heat a heavy skillet (cast-iron preferred) over medium-high to high heat until very hot, about 5 minutes. Add 2 tbs neutral oil and swirl to coat; the oil should shimmer but not smoke heavily.

Sear the steak

Place the steak in the hot pan, presentation side down. Do not move it for 2–3 minutes to develop a deep brown crust. Flip and sear the other side for 2–3 minutes. For a 1.25–1.5" thick 20 oz rib steak, sear times give a good crust before finishing; adjust for thickness.

Baste and finish

Reduce heat to medium. Add 2 tbs unsalted butter, crushed garlic cloves, and thyme sprigs to the pan. Tilt the pan slightly and spoon the melted butter, garlic and thyme over the steak continuously (basting) for 2–4 minutes while monitoring internal temperature: about 120–125°F (49–52°C) for rare, 130–135°F (54–57°C) for medium-rare, 140°F (60°C) for medium. If steak is thick and needs more time, transfer the pan to a preheated 400°F oven for 3–6 minutes, continuing to baste once returned to the stovetop.

Rest

Transfer the steak to a cutting board and tent loosely with foil. Let rest 8–10 minutes to allow juices to redistribute. If using flaky sea salt, sprinkle about 1/2 tsp over the steak while resting.

Slice and serve

Slice the steak against the grain into 1/4–1/2" slices. Serve with a pat of compound butter or steak sauce if desired.

Sautéed mushrooms

Prepare mushrooms

While the steak rests or during its last 5–8 minutes of cooking, heat a separate large skillet over medium-high heat. If you prefer to cook mushrooms in the same pan after the steak, remove excess fat leaving about 1 tbs and continue; otherwise use a clean pan.

Cook aromatics

Add 1 tbs unsalted butter and 1 tsp neutral oil to the hot skillet. When butter foams, add the minced shallot and cook 30–45 seconds until fragrant and translucent. Add the minced garlic and cook another 15–20 seconds, careful not to burn.

Sauté mushrooms

Add the sliced mixed mushrooms (about 10 oz) to the pan in a single layer if possible. Let them sit undisturbed 1–2 minutes to brown, then stir/turn and continue cooking 3–4 minutes until nicely browned and juices mostly evaporate.

Deglaze and season

Pour in 2 tbs dry white wine or sherry to deglaze the pan, scraping up browned bits from the bottom. Cook 1–2 minutes until the liquid reduces slightly. Season with 1 tsp kosher salt and 1/2 tsp freshly ground black pepper. Stir in chopped parsley.

Finish

Taste and adjust seasoning. If you reserved pan juices/butter from the steak, add a small spoonful to the mushrooms for additional richness. Keep warm until the steak is rested and sliced, then spoon mushrooms over or beside the steak when serving.

Finishing (optional)

If using compound butter, place 2 tbs on the hot sliced steak so it melts. Alternatively, serve flaky sea salt on the side. Plate steak slices, top or accompany with the sautéed mushrooms, and serve immediately.