In-N-Out Animal Style Fries

1 cup mayonnaise
⅔ cup ketchup
2 tablespoons sweet pickle relish
1 teaspoon apple cider vinegar
½ teaspoon pepper
½ teaspoon salt
Caramelized Onions:
2 tablespoons olive oil
2 tablespoons brown sugar
1 small yellow onion chopped
1 32-ounce bag frozen straight-cut French fries
2 cups shredded mild cheddar cheese

Place mayonnaise, ketchup, relish, vinegar, salt and pepper in a small bowl and mix until thoroughly combined.
In a frying pan, heat olive oil and brown sugar over medium heat.
Add onion and cook for 10-12 minutes until caramelized, stirring frequently.
Place fries on a baking sheet in a single layer and cook according to package instructions. Make sure not to overcook them.
Remove fries from the oven and top with cheese.
Return the fries to the oven and cook for another 5-7 minutes or until the cheese has melted and fries are starting to brown.
Top the cheese fries with caramelized onions and animal sauce.