Start by washing and peeling your russet potatoes. Cut them into evenly sized fries—about ¼ to ½ inch thick—to ensure they cook uniformly. Pat them dry with a clean kitchen towel to remove excess moisture, which helps achieve crispiness.
Place the cut fries into a large mixing bowl. Drizzle 2 tablespoons of extra-virgin olive oil over them, then sprinkle with Cajun seasoning, garlic powder, dill weed, and onion powder. Toss well to coat every fry evenly. Spread the fries in a single layer on a baking sheet lined with parchment paper or a non-stick surface.
Roast in a preheated oven at 425°F (220°C) for 25-30 minutes, flipping halfway through, until golden and crispy.
While the fries are roasting, melt the unsalted butter in a medium saucepan over medium heat. Once melted, whisk in the all-purpose flour and cook for about 1 minute to form a roux—this eliminates the raw flour taste.
Slowly whisk in the milk, continuing to stir until the mixture thickens and starts to bubble gently, about 3-5 minutes.
Remove the saucepan from heat and stir in the freshly grated sharp cheddar cheese until smooth and melted. If the sauce is too thick, add a splash more milk to reach your desired consistency. Season with a pinch of salt if needed.
Once the fries are perfectly crispy, transfer them to a serving dish. Generously drizzle the cheddar cheese sauce over the fries. For an extra touch, sprinkle chopped chives or green onions on top and serve with ranch dressing on the side, if you like.