Bring the steak medallions to room temperature for 30 minutes. Pat dry thoroughly with paper towels. Season both sides generously with kosher salt (about 3/4 tsp per side total) and freshly ground black pepper.

Sear

Heat a heavy skillet (cast-iron preferred) over high heat until smoking. Add 2 tbs neutral oil and swirl to coat. Place medallions in the pan without crowding; sear 2.5–3 minutes per side for medium-rare (internal temp 125–130°F / 52–54°C). Reduce time by ~30–45 seconds per side for rare, or increase for desired doneness.

Baste & Rest

During the last 60–90 seconds of cooking, add 2 tbs butter, smashed garlic cloves and herb sprigs to the pan. Tip the pan slightly and spoon the melted butter over the medallions (basting) to build flavor and color. Remove medallions to a warm plate, tent loosely with foil and rest 5–8 minutes before serving.

Fingerling Potatoes

While the steak rests (or roast simultaneously), preheat oven to 425°F (220°C). Toss halved fingerlings with 2 tbs olive oil, 1 tsp kosher salt and 1/2 tsp freshly ground pepper so they’re evenly coated. Spread cut-side down on a rimmed baking sheet in a single layer.

Roast for 25–30 minutes until golden brown and tender when pierced with a fork. Shake the pan once halfway through to promote even browning. When done, transfer to a bowl and toss with chopped parsley for freshness. Keep warm until plating.

Jus

After removing steaks, pour off excess fat from the skillet, leaving about 1 tsp and any fond (browned bits). Reduce heat to medium and add 1 tsp olive oil if pan is dry. Add the minced shallot and sauté 45–60 seconds until translucent but not browned.

Deglaze the pan with 1/4 cup red wine, scraping up browned bits with a wooden spoon. Let the wine reduce by about half (~1–2 minutes).

Add 1 cup beef demi-glace (or beef stock) and 1/2 tsp thyme. Bring to a simmer and reduce by about one-third until slightly thickened, 4–6 minutes. Taste and season with 1/4 tsp salt and 1/4 tsp pepper as needed.

Off the heat, whisk in 1 tbs cold butter, one cube at a time, until the jus becomes glossy and slightly thickened. Strain the jus through a fine mesh sieve into a small saucepot or bowl to remove solids for a smooth finish. Keep warm.

Assembly & Serving

Place a portion of fingerling potatoes on the plate. Arrange the rested prime NY medallion(s) beside the potatoes. Spoon 1–2 tbs of warm jus over each medallion and a little around the plate. Garnish the potatoes with extra parsley and optionally finish the steak with a light sprinkle of flaky salt.