In a large skillet, melt 1 tablespoon of butter with 1 tablespoon of neutral oil over medium-low heat. Add 1 cup of diced onions and sprinkle with a pinch of salt. Stir occasionally for about 30 minutes, until the onions are a beautiful golden brown and sweetly fragrant.

In a medium bowl, combine ½ cup mayonnaise, 2 tablespoons ketchup, 1 tablespoon rice vinegar, 1 tablespoon sweet relish, 1 teaspoon sugar, and a dash of chili flakes if desired. Whisk all the ingredients together until smooth.

Preheat your oven according to the package instructions for frozen fries. Spread the fries evenly on a baking sheet and bake for the recommended time, usually around 20-25 minutes, until crispy and golden brown.

Once the fries are out of the oven, sprinkle 1 cup of shredded American cheese over the hot fries. Turn on the broiler in your oven and place the fries back in for about 3-5 minutes, until the cheese is bubbling and melted.

Carefully remove the fries from the oven and transfer them to a serving platter. Layer the sweet caramelized onions over the cheesy fries, then drizzle the homemade special sauce all over the top.