Prepare frozen French fries based on the package instructions. You can bake, fry, or air fry the french fries.
While the fries are cooking, prepare the sauce and fried onions.
In a small bowl, mix together mayonnaise, ketchup, sweet pickle relish, and white vinegar.
Melt butter in a large skillet over medium high heat. Add white onion and sauté the onions in the butter until they are caramelized, about 3 to 5 minutes.
Place the cooked fries on a plate and top with slices American cheese, the caramelized onions, and the sauce.
Serve immediately while warm and enjoy!
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Notes
These fries are best served fresh. You can refrigerate the sauce in an airtight container for up to 1 week.