01 -
Melt butter in a pan over medium-low heat and add the neutral oil. Add the diced onions and salt to the pan. Stir every few minutes until the onions are fully caramelized, turning golden brown and sweet. This process will take at least 30 minutes or longer. If the onions look like they're burning, reduce the heat.
02 -
While the onions are caramelizing, mix all the special sauce ingredients in a bowl: mayonnaise, ketchup, vinegar, sweet relish, sugar, and chili flakes (if using). Stir until well combined and set aside.
03 -
Prepare the frozen french fries according to the package instructions, either by baking or frying until golden and crispy.
04 -
Once the fries are cooked, transfer them to an oven-safe dish. Top with either grated cheddar cheese or American cheese slices. Place under the broiler for 3-5 minutes, or until the cheese is completely melted and slightly bubbly.
05 -
Once the cheese has melted, top the fries with the caramelized onions. Pour the special sauce generously over the top. Serve immediately while hot and enjoy!