Take the Salt and Pepper and mix together. I mixed 1 part salt to 2 parts pepper in a sprinkler spice jar, although as mentioned above I did think this was a bit peppery. Not all of the mixture got used. I added a think coating of the mustard to the beef, to help the salt and pepper adhere, and then put to one side.
I got my Char-Broil Gas to a high temp and then placed the Lodge Cast-iron pan on it with a little Rapeseed Oil. Using a laser thermometer I got the pan to around 320°C, before searing the beef for 2-3 minutes on each side.
I had prepped my Weber Kettle for an indirect cook, and once I had seared the beef I placed on the indirect part of the BBQ, adding an Olive Wood Chunk for some extra smokiness.
Whilst the beef was cooking I prepped the gravy. Start by melting the butter over a medium heat. Add the flour, and mix until the flour is dissolved. Now add the 2 beef Oxo cubes and stir in before slowly adding 400ml of boiling water (directly from the kettle). Mix well and bring to a gentle simmer, then add the Balsamic and Worcester sauce and stir in well. Reduce to a medium heat, and occasionally stir.Tip: you can add some salt and pepper to taste but I would wait until after you have added the bone marrow and beef fat.
Keep checking your meat depending on how well done you would like it. I removed mine at 52-55°C. There was a variance in the temperature throughout the meat. I was quite surprised at how quickly this cooked so had to wrap for longer than planned which took it beyond the ‘doneness’ I was looking for. I wrapped in foil and put it to one side.
The bone marrow had melted and mixed with the fat dripping from the meat. I removed this from the BBQ and added to my gravy mix, again bringing it back to a simmer and stirring well before reducing the heat again. Taste the gravy and decide if you need to add any seasoning.
Unwrap the meat, slice, and serve with all the trimmings, finishing off with the lovely rich bone marrow gravy.