Cheesy Lamb Burger & Truffle Mayo

• While the fries are baking, pick and finely chop rosemary leaves. 
• Thinly slice brown onion.
• In a large bowl, combine lamb mince, fine breadcrumbs (see ingredients), the salt, egg and half the rosemary. Season with pepper.
• Shape the lamb mixture into evenly sized patties (1 per person), slightly larger than a burger bun. Set aside.

• Place Parmesan cheese in even circles (about the same size as your buns, 1 per person) on a second lined oven tray.
• Bake until the cheese is golden and crisp at the edges, 6-8 minutes.
• Remove from the oven and set aside. The Parmesan crisps will harden as they cool.

TIP: Keep an eye on the crisps, they can burn quickly!

• While the crisps are baking, heat a drizzle of olive oil in a large frying pan over medium-high heat. Cook onion and remaining rosemary, stirring, until softened, 4-5 minutes.
• Add the balsamic vinegar, brown sugar and a splash of water and mix well. Cook until dark and sticky, 3-5 minutes. Transfer to a small bowl.

• Wipe out frying pan and return to medium-high heat. Cook the lamb patties until just cooked through, 4-5 minutes each side. 
• Meanwhile, halve bake-at-home burger buns and bake directly on a wire oven rack until heated through, 2-3 minutes. Thinly slice the tomato.