Rub the chicken breasts with a little butter or oil and roast them for 30 minutes in a fairly hot oven, Gas 6 (400°F/200°C). Slice them into thin slices and arrange in a large earthenware dish. Fry the sliced mushrooms gently in two thirds of the butter until only just softened. Fry the flaked almonds in the butter until just golden. Add most of the flaked almonds to the chicken and mushrooms in the earthenware dish but reserve about a quarter of the nuts for final decoration. Sprinkle all with oregano. Keep warm. Make a white sauce by melting the remaining butter in a heavy medium-sized saucepan. Stir in the cornflour until smooth. Fairly gradually add the milk. Bring to the boil and simmer for 3 minutes stirring frequently. Add the grated Cheddar and crushed garlic and stir until melted. Take off the heat and stir in the cream and the egg yolks. Put back on a gentle heat add salt and black pepper to taste and heat up but do not boil. Pour over the chicken, mushrooms and almond mixture. Sprinkle top with grated Parmesan and finally the reserved almonds. Serve, or keep it warm in a low oven until you are ready to eat it. I think this is best eaten with fresh crispy bread and a salad but you could have new potatoes or rice, and broccoli would go very well with the cheesy sauce.