In a small mixing bowl, add all of the sauce ingredients and mix to combine. Set aside.
In a parchment lined sheet pan, spread out fries into an even layer. Preheat oven and bake fries according to package instructions. Alternatively, you can fry or air-fry the fries according to package instructions.
As the fries bake, prepare the caramelized onions. In a skillet over medium heat, melt the butter and add in the diced onions. Season with salt to taste. Sauté the onions in the butter until it becomes softened and light golden brown in color, about 10-12 minutes.
Once fries are done baking, immediately top with slices of American cheese. Residual heat from fries should melt the cheese but if all the cheese does not melt, place sheet pan back into the oven for 3-5 minutes to fully melt cheese.
Top melted cheese with caramelized onions and a generous drizzle of the sauce.
Serve immediately while warm and enjoy!