Prep the steak: coat the steak in the shio koji, transfer to a resealable plastic bag, and marinate at least 2 hours (4–6 is even better), and up to 24 hours in the fridge.

Make the compound butter: add softened butter and herbs to a small bowl and use a spatula or spoon to mix well to combine. Transfer to the center of a piece of plastic wrap, fold plastic wrap over, and mold the butter into a compact log, pressing hard to remove air pockets. Tightly twist the ends of the plastic wrap to form butter into a sausage shape, about 1” in diameter, making sure it is sealed well. Chill until firm, about 1 hour. Compound butter will keep in the fridge for up to 2 weeks and in the freezer for up to 6 months.

Prep the fries: scrub but do not peel potatoes. Using a Chef or Santoku Knife, slice potato lengthwise to create a ¼-⅓”-thick plank. Turn the flat side of potato down onto cutting board to create a stable surface for cutting. Continue slicing potato lengthwise into uniform ¼-⅓”-thick planks. Stack a few planks and slice them lengthwise to form uniform sticks (either ¼ or ⅓”-thick, whichever thickness you chose for the planks). The most important thing is that all the fries are about the same thickness so they will cook at the same rate.

Transfer fries as you cut them to a bowl of cold water, submerging them to avoid discoloration. Repeat with remaining potato. Make sure all fries are submerged in water and soak for 1 hour minimum at room temperature, and up to overnight in the fridge.

Add oil to a depth of about 2 inches in a large Oval Dutch Oven. Heat to 375F. Drain fries and pat very dry using paper towels or a dish towel. Don’t put wet fries into hot oil!

Working in batches, use a spider or slotted spoon to add fries to oil and cook, stirring constantly. Be careful as the oil will bubble up when the fries are added, do not overcrowd the Dutch Oven. Cook until a thin skin forms on the fries but they have not started to brown, 1 ½-2 minutes per batch. Transfer to a Sheet Pan Rack set over a Sheet Pan to drain. Allow fries to cool, about 30–60 minutes.

Ready for dinner? Cook the steak: preheat oven to 400F. Pat steak dry and allow to come to room temperature 30 minutes before cooking.

Heat a large Carbon Steel Frying Pan over medium-high and add 1 Tbsp. canola oil. Just before cooking, season steak generously with salt and pepper on both sides.

Once oil begins to smoke, sear steak in pan on all sides until caramelized and a crust forms, about 3–4 minutes per side.

Transfer pan to oven to complete cooking steak to your desired internal temperature. It should take 3–4 minutes to achieve medium-rare (internal temperature of about 125F).

Carefully return pan to stovetop over medium. Tilt pan toward you and add a 1”-thick slice of compound butter next to the steak, allow to melt and pool to one side. With the pan still tilted, use a large spoon to  baste melted butter over steak continually until butter is no longer bubbling and smells nutty, about 1 minute.

Transfer steak to a Sheet Pan Rack set over a Sheet Pan and allow to rest 10 minutes.

Finish the fries: bring oil back to temperature of 375F and work in batches to fry fries until golden brown, 2–3 minutes per batch. Season immediately with salt.

Arrange steak and fries on a Serving Platter. Top with parsley and flaky salt, if desired.