The goose should be boned. Put the bones in a saucepan, cover with cold water, bring to the boil and skim. Then add the sliced vegetables and the mushrooms. Season with salt’and peppercorns, parsley and dill. Simmer gently for about 1 hour and strain the stock. Chop the mushrooms, mix with the kascha, and stuff the goose with the mixture. Roast the bird, basting with a little of the strained stock and serving this as the sauce.