In a mini chopper blend the bacon rashers until it is minced.
Add the minced bacon to the minced beef and the mustard, season with salt and pepper.
Roll the meat into 100g balls. It should make at least 8 burgers.
Place the rolled meat in the fridge to rest while you make the sauce
In a bowl to make the sauce, mix the mustard, ketchup, mayonnaise and diced gherkins.
Heat up a cast iron pan with a drizzle of oil. Remove the burgers from the fridge. Place the meat in the pan and press down with a spatula. As the are thin burgers they will take a minute to cook on each side. After you have turned over the burger place the cheese on top.
Toast the bun. Spread some sauce on the bottom followed by the lettuce and tomato. place on the 4 burger patties followed by the finely slice onions and top with more sauce.