Preheat & Prep: Set your oven or air fryer to 400°F (200°C).

Crisp the Fries: Arrange the frozen fries in a single layer on a baking sheet or air fryer basket. Cook according to package directions until deeply golden and crispy.

Start the Roux: While fries cook, melt butter in a 2-quart saucepan over medium heat. Whisk in the flour and cook for 2 minutes to remove the raw flour taste.

Infuse Liquids: Gradually stream in the milk, whisking constantly to prevent lumps.

Season the Sauce: Stir in the salt, white pepper, ranch seasoning, and half of the cayenne powder.

Thicken: Reduce heat to medium-low and simmer for 5 minutes, stirring frequently until the sauce coats the back of a spoon.

Melt the Cheese: Fold in the shredded white cheddar using a silicone spoon. Stir until the sauce is completely smooth and creamy (approx. 2–3 minutes).

Assemble: Transfer the hot fries to a platter. Pour the warm cheese sauce over the top.

Final Touch: Dust the remaining cayenne powder over the sauce and serve immediately.