In a large glass bowl mix the ketchup, mayonnaise, gherkin, mustard and a bit of the juice to form a lovely rich sauce. I normally make this the night before as the flavours blend even better but a few hours is enough.
Put the beef mince into a bowl and grate the red onion using the coarse side of a grater. The grated onion will blow your mind.
Add the grated onion to the mince along with a good splash of Worcestershire sauce, the celery salt, and chilli flakes. Mix everything thoroughly with a wooden spatula or your hands.
When fully combined, divide into 8 equal portions.
Flatten each burger portion into a thin patty. They do almost rise in the pan so don't be worried.
Turn the oven to 200C/fan 180C/gas 6 and heat a frying pan on a high heat. (Non stick is best).
Fry each of the patties for about 2 minutes each side. My pan fits four at a time but I place them on a baking tray until they are all cooked.
When they are all fried and on the baking tray, add cheese to each one of them and place in the oven for about 2 minutes to melt the cheese.
Put some burger sauce from Step 1 on each bun base and start to build. Add lettuce and a slice or two of tomato. On top of that place two of the burger patties, add more sauce, then the onions and finally the gherkins. I normally add a little more sauce to the lid on the bun for good measure.
Finally I pin them together with a small kebab stick or whatever you have to hand
Notes
I also add 2 rasher of streaky bacon to he burger for the full effect. I don't eat anything else for the rest of the day so in my view, its a diet.