¼–½ cup vinegar, or as needed for desired consistency
Directions
Preheat your Blackstone griddle to low heat and your air fryer to medium heat.
In a small bowl, whisk together the mayonnaise, ketchup, mustard, relish, onion powder, garlic powder, smoked paprika, and vinegar until smooth. Add more vinegar as needed until the sauce is slightly thin and pourable. Set aside.
Divide the frozen fries between two air fryer baskets and cook according to package directions, or until golden brown and crispy.
While the fries cook, melt the butter on the griddle and add the diced onion. Cook slowly, stirring occasionally, until softened and deeply caramelized, about 15–20 minutes. Season lightly with salt halfway through cooking to help draw out moisture and encourage caramelization.
Once the fries are done, transfer them to a large bowl and toss with Smashburger Seasoning.
Line the air fryer baskets or trays with parchment paper. Divide the fries into an even layer and top each portion with American cheese slices. Return to the air fryer for 1–2 minutes, or until the cheese is fully melted.
Transfer the cheesy fries to serving plates. Top with the caramelized onions and drizzle generously with fry sauce.
Garnish with chopped parsley, if desired, and serve immediately.
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