Mix together the anchovy essence with half of the butter and one tablespoon of the extra-virgin olive oil.
Smear the mixture all over the mushrooms. Place in a roasting dish and cook for 12-15 minutes, when the mushrooms should be just tender.
Meanwhile melt the remaining butter in a heavy-based saucepan.
Add in the chopped onion and cook over a medium heat until just softened, around 3 minutes, then add the garlic and cook for a further minute.
Stir in the butter beans and allow to just heat through.
Place the white, black and pink peppercorns and sea salt in a pestle and mortar and roughly crush. Alternatively place in a plastic bag and use a rolling pin.
Rub the dijon mustard all over the steaks, then tip half the peppercorn mixture onto a plate. Coat both sides of one of the steaks with the salt and pepper mix.
Repeat the process with the other steak.
Heat a heavy-based frying pan until smoking hot, then add in the light olive oil.
Fry for about 2-3 minutes each side depending on thickness and how rare you like your steak. Remove from the pan and allow to rest.
Next add about 2-3 tablespoons of the cream to the butterbeans with the horseradish and season generously with salt and freshly ground pepper.
Blend or mash to a rough puree and then stir in the parsley and chives. You may need to add a little more cream if the mash is too stiff.
Finally over a high heat, de-glaze the steak pan with the sherry, stirring to incorporate all the lovely juices. Stir in the remaining mustard and the cream. Bring to a gentle bubble and thicken slightly.
Serve the steaks with the butterbean mash with the roast mushrooms on one side and a drizzle of the sherry cream sauce. Serve with wilted spinach.