Make the burgers at least an hour before you want to cook them. Divide the mince into 4 portions and work each ball in your hands for a few minutes to melt the fat and mould them into a relatively smooth, round patty. Make them slightly bigger than your bun, as they will shrink when cooked.
Pop them on a tray, cover with clingfilm and chill in the fridge.
When you're ready to cook your burgers, get your toppings ready. Pick off, wash and spin dry the lettuce leaves, cut your cress, slice the apples, crumble the blue cheese into chunks, and leave everything to one side.
Preheat your grill to high. Pop a large non-stick frying pan over a medium heat and add a drizzle of oil to the pan.
Fry the burgers for around 4 minutes on each side if you like them pink in the middle, or longer if you prefer them fully cooked, seasoning the patties with black pepper as you cook them.
Halve and toast the buns under the grill or on a hot griddle, then line them up on a board ready to go.
When the burgers are cooked, top each with the blue cheese and pop under the grill for a couple of minutes until nice and oozy.
Now build your burgers. First layer the salad leaves and apple onto the buns, followed by a good drizzle of mustard.
Pop the burgers on, and top with the cress (a cucumber and chilli relish is great here too). Squish the bun tops on and serve straight away.