Preheat the oven to 55°C/Gas Mark ¼, or as low as you can get your oven.
Make the savoury brandy butter. In a pestle and mortar, grind the juniper, cloves, bay leaf, nutmeg and cracked black pepper to a rough powder. Put the butter into a mixing bowl and beat with a wooden spoon or spatula. Add the ground spices, mustard, brandy, shallot, chervil, tarragon and salt and mix together. If you’re using it, dice the poached bone marrow into small pieces and mix it into the butter.
Lay out a sheet of cling ﬁlm on your worktop and place the brandy butter in the middle of it. Roll up into a sausage shape, about 3cm in diameter, and tie the ends of the cling ﬁlm. Chill in the fridge for 1 hour or so until set. This will keep in the fridge for a week or in the freezer for up to 3 months.
Put the unseasoned rib of beef on to a ﬂat baking tray and place in the oven. Cook for 3 hours, until the internal temperature is 55°C when tested with an instant-read thermometer. Trust me, as long as the oven is at a low enough temperature, this will be amazing!
Take the beef out of the oven and warm a large frying pan over a high heat. Pour in a little oil and the butter for cooking and heat until the butter is foaming. Season the beef heavily with salt and place it in the pan. Cook on a high heat until coloured on one side – this should take approximately 4 minutes. Flip over and colour the other side, again for about 4 minutes. While it’s colouring, put a thick slice of the savoury brandy butter on to the top side and watch it melt.
Take the beef from the pan and serve immediately – there’s no need to rest it as the cooking process has been slow. Serve with fries and a salad, and some more of the brandy butter on the side. Lush!