Cut potatoes into 1/4"–3/8" matchstick fries. Rinse under cold water until water runs clear to remove excess starch. Pat thoroughly dry with kitchen towels — moisture will cause oil spatter and soggy fries.

First fry (blanch)

Heat oil in a deep pot or fryer to 300°F (150°C). Fry the cut potatoes in batches for 4–6 minutes until soft but not browned. Remove with a slotted spoon and drain on paper towels. Let cool while you prepare steak and sauce (or refrigerate briefly).

Second fry (crisp)

Increase oil temperature to 375°F (190°C). Fry the cooled blanched fries in batches for 2–3 minutes or until golden brown and crisp. Drain on paper towels, season immediately with fine sea salt and freshly ground black pepper; toss with chopped parsley if using. Keep warm in a low oven (200°F / 95°C) on a tray while finishing steak.

Béarnaise Sauce

Reduce aromatics

In a small saucepan, combine white wine vinegar, dry white wine, minced shallot, and 1 tablespoon of chopped tarragon. Bring to a simmer over medium heat and reduce until about 2 tablespoons of liquid remain (about 5–7 minutes). Strain into a heatproof bowl and let cool slightly.

Whisk egg yolks

Place the reduced vinegar mixture and egg yolks in a heatproof bowl. Whisk vigorously to combine. Set the bowl over a saucepan of barely simmering water (double boiler), ensuring the bottom of the bowl does not touch the water. Whisk constantly until mixture thickens and becomes pale and ribbon-like — about 3–4 minutes.

Emulsify with butter

Remove bowl from heat. Very slowly stream in the warm melted butter while whisking constantly to create a smooth emulsion. Start drop by drop, then increase to a thin steady stream as the sauce thickens. If sauce becomes too thick, whisk in a teaspoon or two of warm water to loosen. Stir in remaining chopped tarragon, salt, and a pinch of white pepper or cayenne to taste. Keep warm (not hot) until serving; if necessary, sit bowl over warm water off the heat.

Steak

Bring steak to room temperature

Pat the 12 oz NY strip dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper. Let rest at room temperature for 30–45 minutes to ensure even cooking.

Sear and finish

Preheat a heavy skillet (cast iron preferred) over high heat until very hot. Add 1 tablespoon vegetable oil and swirl. Place the steak in the pan and sear undisturbed for 2–3 minutes until a deep brown crust forms. Flip and add 1 tablespoon unsalted butter, crushed garlic cloves, and thyme sprigs. Tilt the pan and spoon the melted butter and aromatics over the steak (baste) for another 2–3 minutes for medium-rare (target internal temp 125–130°F / 51–54°C). Adjust time 1–2 minutes per side for desired doneness. Remove steak to a cutting board and rest 5–7 minutes tented loosely with foil.

Slice and serve

Slice the rested steak against the grain into 1/4"–1/2" slices. Plate with a generous portion of fries and spoon 2–3 tablespoons béarnaise sauce over the steak or serve sauce on the side. Garnish fries with parsley if desired.