Sweet Potato and Celeriac Mash

Cut the vegetables into even-sized chunks and cook in a large pan of boiling salted water for 20-25 minutes, until softened. Drain well. Preheat the oven to 200C / Gas 6 / fan oven 180C. Pour the cream into the pan, warm through gently without boiling, then return the potatoes and celeriac to the pan. Turn off the heat and mash them well, then season generously with salt and pepper. Spoon the mash into a buttered shallow ovenproof dish and form hollows and peaks on the top with the back of a spoon. Dot with butter and grate some nutmeg generously over the top. Bake for 20 minutes from hot or 40 minutes from cold. Serves 6