Beef mince, white onion, cheddar cheese, 1 egg.
2) Finely dice a white onion and fry in a little butter. Stir the onion into the egg and add the beef mince.
3) By hand, mix the ingredients, squeezing the meat until it is integrated.
4) Cut a lump of cheddar and form the burger around it. Wrap in cling film and allow to cool in the fridge for 20 minutes, then bake in the oven for 20 minutes or barbeque. Serve slathered with ketchup.