1. Make the beef burgers by mixing all the burger patty ingredients together in a large bowl. Then form the mixture into four patties. Put onto a tray, cover with clingfilm and refrigerate for 1 hour.
2. Make the ketchup by mixing all the ingredients together in a small saucepan, heat gently & stir for 2 minutes. Allow to cool and put into a serving dish.
3. Remove the burgers from the refrigerator and allow to come to room temperature before cooking.
4. Pour a splash of oil into a large pan.
5. To cook the burgers, heat the oil until smoking and seal the burgers on both sides until browned. Continue to cook in the pan on a medium heat, turning regularly until cooked to your liking.
6. To finish the dish, slice the brioche buns and toast the inside lightly. Spread on the ketchup and top with the burger patty, cheese, lettuce & gherkins.