- STEP 1
Pre-heat the oven to 180 C. Chop the sweet potatoes into wedges and mix in a bowl with some olive oil and the rest of the ingredients. Empty the wedges into a baking dish lined with grease-proof paper and place in the oven, checking occasionally.
- STEP 2
Season the beef mince with salt and freshly ground black pepper and, using your hands, mix in a bowl with the English mustard. Divide the mince into four equally-sized balls and press each one between your palms to form a patty. Place the patties on a plate, cover, and chill in the fridge for 30 minutes.
- STEP 3
Cut the shallots into thin slices. Heat some olive oil in a pan over a low-medium heat and fry the onions with a pinch or two of sugar until golden brown and caramelised. Once done, place the onions in a bowl or container to one side.
- STEP 4
Add some more olive oil to the pan, turn up the heat slightly, and add the beef patties. Cook for around 3-4 minutes on each side. When flipping the patties for the first time, add the cheese slices on top so that they begin to melt.
- STEP 5
Toast the brioche buns, then spread the mayonnaise and Dijon mustard on the bottom half and the tomato chutney/relish on the top half of each bun. Next, add a couple of leaves of lettuce, followed by a couple of slices of tomato and gherkin. Place the beef patties and cheese on top of the salad. Finally, add the caramelised onions on top of the patty, before placing the top half of the brioche bun on top. If the burgers are large, cutting them in half will help.