Juicy Beef Burger with Caramelized Onion and Parmesan Crisps

Pile the grated Parmesan in small circles onto a baking sheet lined with parchment paper. The diameter of the circles should be roughly the same size as the hamburger bun.

Place in an oven preheated to 180°C, and bake for about 5 minutes, until golden brown and crispy. Let cool completely after removing.

Cut the onion into thin half-moons. In a pan, heat the butter with a little oil, so it doesn't burn.