Luxe Hamburger with Truffle-Parm Fries

Bake the brioche bun alongside during the final 2 minutes of cooking time. Meanwhile, slice the onion into half rings and grate the Parmigiano Reggiano.

Melt two thirds of the butter in a frying pan over medium-high heat and fry the portobello for 3 - 4 minutes until evenly browned. Season to taste with salt and pepper, then cover with the lid and fry for another 3 - 4 minutes. Turn off the heat and set aside to keep warm, still covered.

Halfway through the fries' cooking time, melt the rest of the butter in a frying pan over medium-high heat. Fry the burger with the onion for 3 - 5 minutes per side or until done, then keep warm until serving.

Meanwhile, finely chop the parsley. Cut the tomato into wedges and transfer to a salad bowl, along with the arugula. Add the white wine vinegar and drizzle with extra virgin olive oil as preferred, then toss well to combine. Season to taste with salt and pepper. In a small bowl, combine the mayonnaise with half of the truffle oil.