In separate pans, boil your swede and potatoes until tender.
In separate bowls, mash your swede with butter and season and do the same to your potatoes. Set aside.
While your swede and potatoes are cooking, saute the onions and garlic in the rapeseed oil until tender, then add the mushrooms and cook gently for 10-15 minutes until the mushrooms are soft and succulent. Stir in the flour.
Add the red wine and stock and cook at a gentle simmer, with a lid on for 15-20 minutes until the wine and stock have turned into a thick sauce, then season.
While the mushrooms are cooking, preheat the oven to 220c/200cfan/425f/gas mark 7.
Transfer the mushrooms to a casserole dish and top first with the swede and then with the mash. Cook in the oven for 25-30 minutes until the potato topping is golden.
Enjoy with a selection of green vegetables and a glass of rich red wine.