Peel, wash and dice the potatoes. Clean and wash the Brussels sprouts. Pre-cook both in boiling salted water for about 5 minutes and drain. Cut the smoked pork loin into cubes.
Put everything into a greased ovenproof dish. Whisk eggs, mustard, salt, pepper, nutmeg and milk and pour over the mixture. Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for approx. 45 minutes.
Finely crumble the toast bread. Wash the thyme and remove the leaves. Heat butter, add breadcrumbs and thyme leaves, roast briefly and spread on the casserole 15 minutes before the end of cooking time. Remove seeds from tomatoes and dice finely.
Heat the oil and sauté the tomato cubes for about 1 minute. Before serving, spread on the casserole.