Wash and peel the russet potatoes (peeling optional). Cut potatoes into 1/4–1/3 inch sticks for classic fries. Rinse the cut fries under cold running water until the water runs clear to remove surface starch. Transfer to a large bowl of cold water and soak for at least 30 minutes (or up to 2 hours) to improve texture.

Dry and (optional) toss with cornstarch

Drain the potatoes and lay them out on clean kitchen towels or paper towels. Pat very dry. If using cornstarch for extra crispiness, put the dried fries in a large bowl, sprinkle 1 tablespoon cornstarch over them and toss until evenly coated.

Heat oil and blanch (first fry)

In a heavy-bottomed pot or deep fryer, pour in enough neutral oil to reach about 3 inches deep (approximately 5–6 cups for a medium pot). Attach a thermometer and heat oil to 325°F (163°C). Working in batches so you don't overcrowd the pot, add fries and fry for 3–4 minutes until they are softened and pale (no browning). Remove with a spider or slotted spoon and drain on a wire rack or paper towels. Let rest for 10 minutes.

Crisp the fries (second fry)

Raise the oil temperature to 375–380°F (190–193°C). Return fries to the hot oil in batches and fry 2–3 minutes until golden brown and crisp. Remove, drain on a rack or paper towels, and immediately season with 1 1/2 tsp kosher salt and 1/2 tsp ground black pepper while still hot so seasoning adheres.

Serve hot. Transfer fries to a serving platter or baskets and keep warm in a 200°F (95°C) oven if cooking large batches.

Garlic Sauce (Aioli-style)

Prepare the garlic

Mince the garlic cloves very finely or smash into a paste using a microplane or the flat side of a chef's knife with a pinch of salt. Using a paste ensures a smooth, evenly garlicky sauce.

Combine ingredients

In a small bowl, whisk together 1/2 cup mayonnaise, 2 tablespoons sour cream, 1 tablespoon lemon juice, 1 teaspoon extra-virgin olive oil, 1/2 teaspoon Dijon mustard, 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper until smooth. Stir in the minced garlic paste. Taste and adjust salt, pepper or lemon to preference.

Finish and rest

Fold in 1 tablespoon chopped fresh parsley if using. For best flavor marry the ingredients for at least 15 minutes in the refrigerator, then bring back to room temperature before serving alongside the fries.