If using fresh potatoes: wash and peel (optional) russets. Cut into 1/2-inch evenly sized fries. Soak cut fries in cold water for 20–30 minutes to remove excess starch. Drain and pat thoroughly dry with paper towels.

Cook fries

Option A — Frying: Heat 2 cups (or enough) vegetable oil in a heavy pot to 350°F (175°C). Fry fries in batches for 4–6 minutes until golden and crisp. Drain on paper towels and season with kosher salt and black pepper while hot. Option B — Baking: Toss dried fries with 2 tbs oil, spread in a single layer on a parchment-lined sheet. Bake at 425°F (220°C) for 25–30 minutes, flipping halfway, until golden and crisp. Season with salt and pepper.

Caramelized onions & jalapeño

Caramelize onions

Heat 1 tbs butter in a skillet over medium-low heat. Add the thinly sliced onion and 0.25 tsp salt. Cook, stirring occasionally, 12–18 minutes until soft and golden brown. If onions dry or stick, add a splash of water. Stir in 0.5 tsp brown sugar and 0.5 tsp apple cider vinegar in the last 1–2 minutes to deepen flavor and deglaze the pan.

Cook jalapeño

Push the onions to the side, add the remaining 0.5 tbs butter if needed and the thinly sliced jalapeño. Sauté 1–2 minutes until slightly softened but still bright (cook longer if you want milder heat). Mix jalapeño with the caramelized onions and remove from heat.

Special sauce

Combine 1/4 cup mayonnaise, 2 tsp ketchup, 1 tsp sriracha, 1/2 tsp Dijon, 1/4 tsp smoked paprika, 1/4 tsp garlic powder, 1/2 tsp lime juice and 1/8 tsp salt in a small bowl. Whisk until smooth. Taste and adjust heat or acidity as desired. Refrigerate until ready to use.

Assemble & finish

Assemble

Arrange hot fries on a large baking sheet or serving platter. Evenly distribute the caramelized onion and jalapeño mixture over the fries.

Add cheese

Scatter shredded cheddar and Monterey Jack (or mozzarella) over the fries. Place under a broiler for 1–2 minutes or in a hot oven (425°F / 220°C) for 3–5 minutes until cheese is melted and bubbly. Watch closely to avoid burning.

Finish & serve

Drizzle the special sauce over the melted-cheese fries (or serve the sauce on the side for dipping). Sprinkle sliced green onions and chopped cilantro over the top. Serve immediately while hot and crispy.