Bring a large pot of water to a rolling boil over high heat. If using fresh-cut fries, blanch them for 2 to 3 minutes, then drain and pat dry.

Fry the fresh-cut potatoes in oil heated to 350°F until golden and crispy, or cook frozen fries as directed on the package. Drain on paper towels and sprinkle with salt.

Melt the butter in a small saucepan over low heat. Whisk in the flour and cook until smooth, about 1 minute.

Gradually whisk in the milk and keep stirring until the sauce thickens.

Stir in the cheddar and pepper jack until melted and creamy. Add a splash more milk if it's too thick, season with salt and pepper, and take off the heat.

In a small bowl, stir together the ranch dressing, hot sauce and Cajun seasoning until thoroughly blended. Set aside.

Pile the fries on a serving plate and drizzle with the warm cheese sauce.

Drizzle with the spicy ranch mixture and top with chopped green onions, if desired.

Serve hot and crispy right away.