Wash and peel the russet potatoes (peel optional). Cut into 1/4 to 1/3-inch thick sticks for classic fries. Keep pieces uniform in size for even cooking.

Rinse the cut potatoes under cold running water until the water runs mostly clear to remove surface starch.

Place the rinsed potato sticks in a large bowl and cover with the cold water. Stir in 1 teaspoon of the kosher salt. Soak in the refrigerator or at room temperature for at least 30 minutes, preferably 1 hour. This helps remove more starch and yields crisper fries.

After soaking, drain the potatoes and spread them on clean kitchen towels or paper towels. Pat thoroughly dry. Leaving moisture will cause oil splatter and reduce crispness.

Toss the dried fries in 1 tablespoon cornstarch until lightly and evenly coated. This creates an extra-crispy exterior. If any clumps form, separate with your fingers.

First (blanch) fry — low temperature

Heat vegetable oil in a heavy pot or deep fryer to 325°F (160°C). If you don't have a thermometer, heat until a small piece of potato sizzles gently and rises slowly. Fry the potatoes in batches (do not overcrowd) for 4–5 minutes until pale and just tender but not browned. Use a slotted spoon to transfer to a wire rack or paper towel-lined sheet to drain. Let cool at least 10 minutes.

Second (crisp) fry — high temperature

Increase oil temperature to 375°F (190°C). When hot, return the cooled fries to the oil in batches and fry for 2–3 minutes until golden brown and crisp. Remove with a slotted spoon and transfer to a wire rack or paper towel-lined tray. Immediately sprinkle with remaining 1 teaspoon kosher salt while fries are hot so the salt adheres.

Cheese and topping

While the fries are hot and just out of the oil, arrange them on an oven-safe platter or cast-iron skillet in a single layer or slightly piled.

Sprinkle the shredded cheddar evenly over the fries so most fries get cheese coverage. If using, also grate Parmesan on top.

Place the platter under a broiler set to high (or in a preheated 450°F / 230°C oven) for 1–3 minutes, watching carefully, until the cheese is melted, bubbly, and just starting to brown. Remove promptly to avoid burning.

Finish with chopped fresh parsley and a grind of black pepper. Serve immediately so cheese stays melty.

Sauce

While fries are cooking, make the sauce: in a small bowl whisk together mayonnaise, ketchup, Dijon mustard, Worcestershire sauce, smoked paprika, garlic powder, lemon juice, and 1/4 teaspoon salt until smooth and homogenous.

Taste and adjust: add more lemon for brightness, more ketchup for sweetness, or more paprika for smokiness. Transfer to a serving bowl or squeeze bottle.

Serve the hot cheesy fries with the sauce on the side for dipping or drizzle some sauce over the fries before adding parsley, if preferred.