Winter Vegetable Gratin

• 1 lb / 455 g celeriac
• 1 lb / 455

Peel and slice all the vegetables. Bring the stock, bay leaf, and spices to the boil, and cook the vegetables in it for 8–10 minutes, adding more boiling water, if necessary. Meanwhile, mix the cornflour and water and stir it into the yoghurt. Bring to the boil and simmer for 5–8 minutes, thus stabilizing the yoghurt. Remove from the heat. Transfer the vegetables to a lightly oiled or buttered