Cook the pasta in boiling salted water for about 10 minutes. In the meantime clean and wash the leek and cut it into pieces of about 3 cm. Heat the fat in a pan and fry the leek in it. Season with salt and pepper.
Cover and cook over a low heat for about 5 minutes. Drain the pasta and let it drain. Wash and clean the tomatoes and cut into thick slices. Layer pasta, leek and tomatoes in an ovenproof dish.
Wash oregano, dab dry and pluck off the leaves. Mix tomato paste with broth and oregano. Season with salt and pepper. Pour the tomato stock over the casserole and bake in the preheated oven (electric range: 200 °C/ gas: level 3) for about 20 minutes.
Whisk milk and eggs. Mix with salt and nutmeg and pour over the casserole. Halve the olives and remove the seeds. Crumble the feta cheese and spread it on the casserole with the olives. Bake for another 10 minutes.