Potato and mushroom stew

• 1 kg (2 lb) potatoes
• 1 tablespoon dried celery or pars

Peel and slice the potatoes and put them in an earthenware casserole. Cover with the herbs, mushrooms and chopped onion. Melt the lard and pour it over the top; add the peppercorns, mix well, cover tightly and place in a pre-heated moderate oven (180°C, 350°F, gas mark 4) to cook for