Preheat the oven to 220C, fan-forced. Line a large oven tray with baking paper. Thinly slice the unpeeled potatoes, stack the slices, then cut into matchsticks. Put the potato on the lined tray, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Bake on the upper oven shelf, turning halfway, for 25-30 mins until golden and tender.
Step 2 — Prep ingredients
Meanwhile, finely chop the onion. Thickly slice the tomato. Trim the lettuce, then thinly slice the leaves. Cut the buns in half. Thinly slice the cheese. Combine 3 tsp olive oil and 1 tsp balsamic vinegar in a large bowl and season with salt and pepper.
Step 3 — Cook patties
Heat 1 tsp olive oil in a medium frypan over medium-high heat. Add the beef patties to the pan, season with salt and pepper, then cover and cook for 4 mins each side or until cooked through. Drain the oil from the pan. Add 1½ tbs barbecue sauce and cook, turning, for 1 min or until the patties are coated. Remove from the pan and keep warm. Wipe the pan clean.
Step 4 — Caramelise onion
Heat 2 tsp olive oil in the same pan over medium-high heat. Cook the onion, stirring occasionally, for 5 mins or until soft. Add 2 tsp barbecue sauce and 1 tsp balsamic vinegar and cook, stirring, for 1-2 mins until the onion is caramelised. Remove the pan from the heat.
Step 5 — Toast buns
While the onion is cooking, put the buns on an oven tray, cut-side up, and bake on the lower shelf for 5 mins or until lightly toasted. Top the fries with the cheese and bake for a further 5 mins or until melted.
Step 6 — Serve up
Add half the lettuce to the balsamic dressing and toss to coat. Scatter the cheesy fries with the onion and drizzle with half the burger sauce. Spread the bun bases with the remaining burger sauce. Layer with the beef patties, tomato and remaining lettuce, then sandwich with the tops. Serve with the loaded fries and dressed lettuce. Enjoy!