Preheat your oven or air fryer to 400°F: Whether you are using the oven or an air fryer, make sure the cooking appliance is thoroughly preheated to ensure even cooking.
Arrange fries: Place the 26 ounces of frozen French fries on a baking sheet or in the air fryer basket, cooking as directed on the package or following the air fryer instructions.
Prepare the cheese sauce: In a saucepan, melt 2 tablespoons of butter over medium heat. Once melting, whisk in 2 tablespoons of flour and cook for about 2 minutes until thickened.
Add milk: Gradually stir in 2 cups of milk, whisking continuously until the mixture is smooth and well combined.
Season the sauce: Add ½ teaspoon of salt, ¼ teaspoon of ground pepper, 2 teaspoons of ranch seasoning powder, and ¼ teaspoon of cayenne powder to the sauce, mixing thoroughly to incorporate the flavors.
Thicken the sauce: Reduce the heat to low and cook, stirring frequently, for about 5 minutes until the sauce thickens further.
Add cheese: Stir in 8 ounces of shredded white cheddar cheese until it is completely melted and the sauce is creamy. Remove from heat and set aside.
Combine and serve: Once the fries are golden and crispy, transfer them to a serving platter. Drizzle the rich Cajun ranch cheese sauce over the fries, and sprinkle with any leftover cayenne pepper for an extra kick. Serve warm for a delightful treat!