Preheat the oven to 200°C.
Boil the potatoes in a saucepan of salted water until tender.
Drain the potatoes and mash them in a bowl with butter and parsley.
Blend bread, blue cheese, and sage in a food processor and press onto one side of the seasoned steak.
Fry the steak crust-side up in olive oil until the bottom is brown, then roast in the oven for four minutes.
Sauté chopped garlic in butter and oil for one minute.
Reduce the red wine by half in the pan, then simmer with mushrooms and carrots.
Serve the steak on top of the mash and drizzle with the mushroom sauce.