Step 1:
finely chop the onion and mix into the mince with the egg. Step 2:
divide into portions and pat into rounds on a floured board. Step 3:
put a cheese triangle into the middle of each one and carefully mould mince round the cheese so its completely surrounded. Step 4:
put into fridge while you preheat oven 200c for 10 mins. Step 5:
put burgers onto an oven tray and cook for 20-25 mins. Step 6:
this might be longer depending on how thick you made your burgers!