Preheat your oven or air fryer to 400°F (200°C). Prepare the frozen fries on a baking sheet or air fryer basket.

Spread the frozen fries evenly and cook according to package instructions, typically 20-25 minutes, until golden brown and crispy.

In a medium saucepan, melt the butter over medium heat, then whisk in the flour and cook for 1-2 minutes.

Gradually add the milk while whisking continuously until thickened, about 3-5 minutes. Season with ranch powder and cayenne pepper.

Lower the heat and stir in the cheddar cheese until melted and creamy. Add milk if a thinner consistency is desired.

Transfer the cooked fries to a serving platter and drizzle with the cheese sauce. Sprinkle with extra cayenne pepper if desired.