Remove the steak from the fridge an hour before you want to cook it. Preheat the oven to 200°C/gas mark 6.
To begin, roast the garlic for the sauce. Slice the top off the bulb to expose the tops of the cloves, drizzle the bulb in a little oil, season with salt and wrap in foil. Place on a baking tray and roast for 35–45 minutes, until the cloves are soft.
To make the beer and bone marrow sauce, melt the butter in a saucepan and gently cook the shallots for 5–10 minutes, or until they’re light golden in colour.
Add the beer and leave to bubble and reduce for a few minutes.
Remove from the heat and whisk in 6 cloves of the roasted garlic and the mustard. Add the beef stock and sherry vinegar, bring to a simmer then reduce by half.
Add the bone marrow and allow to melt – it won’t melt completely but will leave some lovely wobbly bits. These are good. Season with salt to taste.
To cook the porterhouse steak, heat a large, heavy-based pan like a cast iron skillet over a medium-high heat. Pat the steak dry and season very generously with salt and pepper (this is a thick steak and you need to season heavily).
Coat the bottom of the pan with a neutral cooking oil (such as groundnut oil) and place the steak in the pan, allowing it to build up a crust for a couple of minutes. Turn and cook until a deep crust has formed on the other side.
Continue frying, turning occasionally, until cooked to your liking, adding a generous knob of butter and basting the steak with it towards the end of cooking. A medium-rare steak will read 40°C on a temperature probe inserted into the centre of the steak.
Remove the steak from the pan and cover with foil. Allow to rest for 10 minutes before slicing and serving with the beer and bone marrow sauce and chips.
Recipe courtesy of www.greatbritishchefs.com