Peel and slice the potatoes into thin pieces.

Soak the potato slices in cold water for 30 minutes.

Heat vegetable oil in a deep fryer or large pot to 350°F (175°C).

Pat dry the potato slices with paper towels and fry them in the hot oil until crispy.

Remove them from the oil and place them on paper towels. Sprinkle with salt.

Combine mayonnaise, ketchup, mustard, pickle relish, vinegar, and sugar in a bowl. Mix until smooth.

Chill the sauce in the refrigerator until ready to use.

Warm the vegetable oil in a small saucepan.

Put in the chopped onions and a pinch of salt.

Cook the onions, stirring occasionally, until they turn brown, which usually takes around 20 minutes.

Preheat your oven to 400°F (200°C) and line a baking sheet with aluminum foil.

Arrange the fries on the baking sheet and sprinkle shredded cheese on them.

Place the fries in the oven and bake for 5-7 minutes, until the cheese is melted.

Remove the fries from the oven, drizzle the sauce over them, and sprinkle the cooked onions on top.

For crispier fries, try frying them twice. Start with a high temperature, then lower it to prevent burning.

Experiment with the sauce ingredients, like mustard, relish, or vinegar, to suit your taste preferences.

If you're short on time, you can cook the onions at a higher heat, but be careful not to let them burn.