Slice the burger buns in half, then toast or grill the cut sides and set aside. Heat the oven to 100C/80C fan/gas 1/4.

Divide the mince into four loose piles and season generously with salt. Heat 1/4 tbsp oil in a heavy frying pan or skillet over a high heat and put one of the piles in the pan. Working quickly, cover with a square of baking parchment and use a second smaller pan to press the beef patty down as hard as you can (you may wear oven gloves or use the end of a rolling pin for pressing down, being careful of the heat and rising steam). Allow to cook for 2 mins.

Remove the parchment and turn the patty over. Press down with a spatula, cover with a slice of cheese and cook for 1 min. Transfer to a baking tray and keep warm in the oven while you cook the other burgers in the same way.

To assemble the burger, scatter a bun base with onion, lettuce and tomato slices, followed by a smashed patty, gherkin slices and the bun top. Serve with your chosen sauces on the side.