Poach the bone marrow in the chicken stock. Once tender, store the marrow in ice water. When the bone marrow has cooled, cut it into small pieces.
Using two separate bowls, make two mixtures for the two different patties: Combine the lean mince with 50g of bone marrow in one bowl and, in the other, the short-rib mince and the other 50g of bone marrow.
Mix the bone marrow and mince together in their two separate bowls and season with salt and pepper.
Turn your griddle on so it gets extremely hot.
Pre-heat the oven to 200 degrees Celsius.
Slice your cheese into +- 2cm thick slices and set aside.
Make 55g balls out of the two different mince mixtures.
Place 4 balls made of the short rib mixture onto the griddle. Take a solid metal spatula and compress until flat. Flip over after about a minute and place the cheese on the already-cooked side before transferring them to the oven. Remove them once the cheese has just melted.
Now, using the lean mince balls, do the same thing then place them on top of the short-rib patties.
Black Garlic Mayonnaise
Combine the mayonnaise and the black garlic puree. Season with salt and pepper, to taste.
Red Cabbage Slaw
Boil and refresh your raw mustard seeds 8 times to remove all impure flavours. Make sure to change your boiling water each time and refresh in ice water every single time.
Bring the vinegar, water and sugar to boil then add the refreshed mustard seeds and let it cool.
Julienne your red cabbage, then add some pickling liquid and mustard seeds to taste.
Season with salt and pepper.
In 180 degree Celsius oil, deep-fry the skinny fries until crispy. Season with truffle zest and salt, to taste.
Cut the burger buns in half and toast on the griddle. Smear the black garlic mayonnaise on both halves of each bun. Slice the roma tomatoes very finely and place them on the bottom bun. Top with the lettuce. Place the hot ultrasmash patty on top of the lettuce and top with the red cabbage slaw, red onion and the bacon.
Serve with truffle fries on the side.
Watch Greg in action, making the burger: