1. Peel the potatoes, wash them, cut them in big dice.
2. Peel the leeks, wash them, remove almost all the green part and cut into pieces 2 cm long.
3. Melt butter in a pan.
4. When the butter is hot, make the leeks slowly, without letting them take color.
5. Wet with water, add the potatoes.
6. Season and cook for 30 minutes.
7. Add milk and serve hot on finely chopped pieces of stale bread.