Melt half the butter in a flameproof casserole and fry the mushrooms for 10 minutes. Lift out and set aside. Melt the remaining butter in the casserole and fry the onion and swede for 8–10 minutes until beginning to colour. Add the flour and cook, stirring, for 1 minute. Blend in the ale, then the stock. Bring to the boil and add the pearl barley, mustard and rosemary. Cover and cook in a preheated oven, 180°C (350°F), Gas Mark 4, for 50 minutes to1 hour until the barley is tender.
Make the cobbler. Place the flour in a food processor, add the butter and process until the mixture resembles breadcrumbs. Add the Gruyère and milk and process to a thick dough, adding a dash more milk if dry. Tip out on to a floured surface and roll out to 1.5 cm (¾ inch) thick. Cut out rounds using a 4 cm (1¾ inch) cutter, re-rolling the trimmings. Increase the oven temperature to 220°C (425°F), Gas Mark 7. Stir the mushrooms and cream into the casserole and check the seasoning. Arrange the scones around the edge and brush with milk. Return to the oven, uncovered, for 20–25 minutes until golden.