Slice open the buns, and spread a thin layer of mustard on both sides. Cut Castello Tickler Extra Mature Cheddar into slices and place slices on both sides. I used about 3 slices per bun. Warm them in the oven at 200°C until the cheese has melted.
Season the meat with salt and pepper. Fry in a hot pan (or on the barbecue). Cook for approx. 2-3 minutes on each side, depending on thickness.
On the bottom bun, layer salad leaves, onions, tomato and then the meat. On the top bun, add a bit more mustard and ketchup. Pop it on top and enjoy your burger!