A slightly healthier but just as tasty spin on the classic from the fast food chain. We use 2 baking sheets, as it's important not to crowd the pan for crispy oven fries.
Preheat the oven to 400F. Slice the potatoes into french fries shapes, roughly 1 cm thick. Transfer the fries into a bowl of cold water as you work, and let sit several minutes to remove some of the excess starch from the outside. Once complete, drain the fries and dry them completely with a tea towel. Dry the bowl they were in, and transfer the fries back, tossing them with 2 tbsp oil and the cornstarch, until all fries are evenly coated.
Prepare 2 baking sheets by adding 2 tbsp oil in the bottom of the pan and preheating the oiled sheets in the oven for a minute or two. Divide the potatoes evenly between both sheets, being sure not to crowd. Bake on 400 for 15 minutes, before removing and turning with a metal spatula, then turn up the heat to 425F and baking for an additional 15-20 minutes or until nicely golden and crispy.
While the fries are baking, prep the cheese sauce. In a microwave safe bowl, melt 2 tbsp butter and add the flour. Return the mixture to the microwave and cook for 30 second intervals, stirring with a fork until the mixture bubbles up and forms the base of a roux (about 2-3 times). When ready, slowly whisk in the milk, stirring very well to incorporate fully with no lumps. Continue to microwave the mixture at 30 second intervals with stirring in between until the mixture is thick enough to coat the back of a spoon. At this point, add the cheese and stir well until the cheese is melted and the sauce is smooth. You may need to microwave for an extra 30 seconds if the cheese doesn't completely melt. Once complete, add the hot sauce and stir well.
To assemble the fries, divide into servings and top each with a good drizzle of cheese sauce, a large dollop of sour cream, followed by tomatoes, then green onions on top. Serve immediately.