French dip burger with bourbon onions

Strain the soup into a medium pan, reserving the onions for topping the burger later. Bring to a low simmer for 10-15 minutes, stirring occasionally, until the soup has reduced by half and is thick enough to coat the back of a spoon. Remove from the heat and stir in 10g of the butter and the Worcestershire sauce; season.

While the sauce is reducing, heat the oil in a large, lidded frying pan over a medium heat and cook the burgers for 4 minutes on one side, seasoning the uncooked side. Flip the burgers over and cook for a further 3½ minutes. Reduce the heat to low, put the cheese slices on top of the burgers and pour 1 tbsp water directly into the pan (not onto the burgers), then top with a lid. Once the cheese is melted and the burgers are cooked through, the juices run clear and no pink meat remains, transfer to a plate to rest.

Return the pan to the heat and toast the buns in the beef fat for about a minute, until golden brown, then transfer to a plate. Turn the heat under the frying pan to high and melt the remaining 25g butter. Add the reserved onions and bourbon and stir quickly to heat through; season. Slather Dijon mustard on the bottom of the buns, if liked, then top with the burger, the bourbon onions and some crispy fried onions, if liked. Serve with the onion sauce alongside for dipping.