Clean, wash and cut the leek into rings. Prepare spaetzle in boiling salted water according to package instructions. Add leek for the last 3 minutes. Wash the smoked pork, dab dry and cut into cubes.
Heat the oil in a pan, fry the meat briefly while turning, remove. Whisk eggs and milk, season with salt, pepper and nutmeg. Drain spaetzle, leek and corn, let drain. Mix with the Kasseler.
Grease 1 large, flat casserole dish or 4 small casseroles. Pour in the spaetzle mixture and pour egg milk over it. Let it simmer in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: level 3) for 20-30 minutes.
Cut the rind off the white bread. Crumble the bread finely. Melt butter and turn the crumbs in it. Sprinkle over the casserole 10 minutes before the end of cooking time.