Preheat oven to 200C/400F/Gas 6.
Bring a saucepan of salted water up to the boil. Add the potatoes and boil until tender.
Drain the potatoes and place into a bowl. Add the butter and mash together. Stir through the parsley. Keep warm.
Place the bread, blue cheese and sage leaves into a food processor and blend together. Press the cheese mixture onto one side of the steak. Season with salt and freshly ground black pepper.
Heat the olive oil in an ovenproof frying pan over a high heat and fry the steak, crust side up, until brown on the bottom. Transfer into the oven to finish cooking for four minutes.
Heat the oil and butter in a frying pan. Add the garlic and cook for one minute.
Add the red wine and cook to reduce the wine by half. Add the mushrooms and simmer for two minutes. Add the baby carrots and simmer for a further three minutes. Stir through the chopped parsley.
To serve, place the mash into the centre of a serving plate, place the steak on top and drizzle over the sauce.