Cut potatoes into 1/3–1/2 inch (8–12 mm) sticks for fries. Place cut fries into a large bowl of cold water and rinse until the water runs clear to remove surface starch.

Soak

Cover the rinsed fries with fresh cold water and soak for at least 30 minutes, up to 2 hours, in the refrigerator. This removes extra starch and yields crisper fries. Drain and pat completely dry with clean kitchen towels or paper towels.

Toss with cornstarch

Place the dried potato sticks in a large bowl, sprinkle the cornstarch evenly over them, and toss gently to coat each fry lightly. This helps create a crisp exterior.

Blanch (first fry)

Heat oil in a deep pot or fryer to 325°F (163°C). If you don't have a thermometer, heat until a cube of bread browns slowly in about 60 seconds. Working in batches, fry the coated fries for 4–5 minutes until they are cooked through but not browned. Remove with a slotted spoon and drain on a wire rack or paper towels. Season lightly with the 1 tsp fine sea salt while warm.

Rest

Let the blanched fries cool for 10–15 minutes. This rest lets steam escape and improves final crispness.

Crisp (second fry)

Increase oil temperature to 375°F (190°C). Fry the cooled fries in batches for 2–3 minutes until golden brown and crisp. Remove and drain on a wire rack or paper towels. Immediately sprinkle with flaky sea salt to taste and a little freshly ground black pepper.

Seasoning & Finish

Melt butter

While the fries are finishing their second fry, melt the unsalted butter in a small saucepan over low heat or in a microwave in short bursts until just melted. Remove from heat.

Combine with truffle oil

Stir the black truffle oil into the melted butter until homogenous. This creates a glossy, aromatic finishing oil. Taste a small dab on a spoon and adjust ratio if desired (start with the listed 2 tbs of truffle oil and increase only slightly if you prefer a stronger aroma).

Toss fries with truffle butter

Place the hot, drained fries in a large warmed bowl or back in the frying basket. Drizzle the truffle-butter mixture over the fries while hot and toss gently but thoroughly so the fries are evenly coated. The residual heat will help the flavors adhere.

Add Parmesan and garnish

Immediately sprinkle the grated Parmesan over the tossed fries and toss briefly to distribute the cheese, which will slightly melt on contact. Finish with the chopped parsley (optional) for color and an extra pinch of flaky sea salt or black pepper if desired.

Serve

Transfer the truffle fries to a serving platter or basket lined with paper. Serve hot, with extra grated Parmesan and a small dish of ketchup or garlic aioli on the side if desired.