01 -
Melt butter in a pan over medium-low heat and add neutral oil. Add the minced onions and salt to the pan. Stir every few minutes until the onions caramelize to a golden brown, about 30 minutes. If onions appear to be burning, reduce heat.
02 -
Combine mayonnaise, ketchup, vinegar, sweet relish, sugar, and chili flakes in a bowl. Mix thoroughly and set aside.
03 -
Bake or fry the frozen fries according to package instructions until crispy and golden.
04 -
Arrange cooked fries on an oven-safe dish, top with grated cheddar or sliced American cheese, and broil for 3-5 minutes or until cheese is completely melted.
05 -
Top the cheese-covered fries with caramelized onions and pour the special sauce over everything. Serve immediately while hot.