400g of the best steak mince you can find, about 10% fat is perfect, go to your local butchers and ask although supermarket is fine but use really fresh rich red coloured mince
125g of bone marrow, again ask your butcher for this
1 white onion, very finely chopped
3 burger buns, you can use any you like but i go for a chewy white bap or brioche bun for this
3 large dollops of good mayo. Again any will do but if you are making this recipe, it's a nice idea to really splurge on a great quality top shelf mayo for this
3 thin slices of large beef tomato
3 slices of good swiss cheese, cheddar will do or anything you have really but please no ‘easy singles’. The nutty flavour of swiss, edam or monterey jack if you can find it is ideal. If your feeling really fancy, grab ask for slices of Kaltbach or Appenzeller from the cheese counter
3 leaves of baby gem or romaine lettuce
1 dash of olive oil
A drizzle of truffle oil if you have it (totally optional, not at all necessary and completely your choice, depends if you like the flavour), most good supermarkets have it now or artisan food stores.
Sea salt to season
Black pepper to season
Heat the butter in a small pan over a medium heat and sauté the onion for 2-3 minutes - or until soft but not coloured. Leave to cool
Mash the bone marrow with the back of a spoon or fork and throw on top of the onion to soften slightly.
If you have them, wear rubber gloves and in a large mixing bowl, mash the onion, marrow and mince with generous seasoning of sea salt and black pepper until the marrow and onion is really well incorporated. Shape into 3 patties, this will easily make 4.
Put on a plate in the fridge for about an hour to firm up
Heat the oil in a large pan and cook the burgers over a medium heat for 3 minutes on each side for medium rare (cook for longer if you prefer your burgers more well done). Remove the burgers from the pan and place the cheese atop to melt, cover and allow to rest
Put the slices of bun or bap into the pan and toast for a minute on each side until they soak up all the juices and turn crisp and golden.
Mix the drizzle of truffle oil into the mayo if desired (go super easy, just half a tsp to start and then adjust if desired, we only want the faintest of flavour so as not to over power the burger and cheese)
Lay a dollop of mayo/truffle mayo on each bottom bun, then a slice of tomato, then a burger on top and finally a leaf of lettuce. Place another small dollop of mayo on the top bun and place on top of the burger. Best Burger you'll ever eat!