Set your oven or air fryer to preheat at 400°F.
Spread the frozen fries out evenly on a baking tray or in an air fryer basket and cook them until they turn golden and crispy following the package directions.
Melt the butter in a medium saucepan over medium heat, then stir in the flour and keep whisking for around 2 minutes until it forms a smooth paste.
Slowly pour in the milk while continuously whisking to avoid lumps, then mix in the salt, white pepper, ranch seasoning, and half of the cayenne powder.
Reduce the heat to medium-low and let the sauce thicken, stirring occasionally, which should take about 5 minutes; once thickened, fold in the shredded white cheddar cheese until it melts into a creamy sauce.
Drizzle the cheese sauce evenly over the cooked fries, sprinkle the remaining cayenne powder on top, and serve immediately while warm.
