Tomato and Couscous Gratin with Yogurt Dip

Peel celery, onions and parsnip, chop finely. Heat 3 tablespoons of butter in a saucepan and saute onions until soft, add the rest of vegetables with raisins and saute briefly. Add vegetable stock and bring to a boil, add couscous and season with salt, pepper and cumin powder. Remove from heat and let stand for 10 minutes. 

Blanch half of tomatoes in hot water, rinse in cold water and peel, halve and remove seeds, dice. Add to couscous together with parsley and mix well.

Separate eggs. Whisk egg yolks with sour cream until smooth. Add to coucous mixture. Beat egg whites until stiff and fold into couscous mixture. Spread couscous mixture in a greased baking dish. Rinse and slice remaining tomatoes and spread on top of gratin. Bake in preheated oven at 180°C (approximately 350°F) for about 45 minutes.