Step 1

Cook the fries according to the manufacturer's directions.

Step 2

Meanwhile, melt the butter and add the oil to a large frying pan and cook the onions over a medium heat, stirring frequently.

Step 3

Lower the heat slightly and add the sugar and salt. Stir every now and then.

Step 4

Continue to cook the onions until they are caramelized. In total, this should take 15-20 minutes.

Step 5

While the onions are cooking, make the sauce. Place all the ingredients in a bowl and mix until everything is well incorporated.

Step 6

Once the fries are cooked, remove from the oven and immediately top with cheese, arranged in a single layer.

Step 7

Top the cheese with the caramelized onions, distributing them evenly.

Step 8

Lastly, top with as much or little sauce as you like.

Step 9

Serve with burgers. Dig in and enjoy!