Season the lamb mince well with salt and pepper, then work into four patties. Put in the fridge for 10 minutes to allow them to firm up.
Put a griddle pan on a high heat. When it’s really hot, add your burgers. They’ll need cooking for about 6 minutes on each side.
In the meantime, cut the burger buns in half. Put the cheddar cheese on the bottom halves and put the buns in the oven, open, at 170 degrees Celsius for 3 minutes.
When the burgers are nearly cooked, top each one with blue cheese for the last minute of cooking.
To compile, squeeze a little ketchup onto the cheesy bun base. Then add your burger and top with a generous handful of watercress before topping with the top of the bun. Delicious!