How to Make It
Preheat the oven to 450°. Spread the fries on a large rimmed baking sheet. Bake for about 20 minutes, until crisp.
Meanwhile, in a medium saucepan, heat the oil. Add the bratwurst and cook over moderately high heat, stirring, until browned in spots, 5 minutes. Using a slotted spoon, transfer to a bowl. Add the 1 cup of onion to the saucepan and cook, stirring, until softened. Stir in the flour to coat. Gradually stir in the milk and bring to a boil. Simmer over moderately low heat until slightly thickened, about 7 minutes. Remove from the heat. Stir in 1 cup of the cheese. Season with salt and pepper.
Mound the fries in the middle of the baking sheet and spoon the sauce on top. Scatter the bratwurst and the remaining cheese on top. Bake for 7 minutes, until the cheese is melted. Sprinkle with red onion and parsley. Drizzle with curry ketchup and serve right away.
Curry ketchup is a simple combination of ketchup and ground curry powder. Look for it at most supermarkets.