I didn't know here existed.
Thanks @Mikiesboy.
So the other day I made leeks potatoes casserole.
It's really easy, peel the potatoes and cut them in thin slices, and then cut the leeks in thin slices l. Put a layer of potatoes then leeks. Then potatoes. If you have more space add another leeks potatoes layer.
For the sauce mix cream, eggs and milk then add the spices you like such as salt, pepper and garlic . Then add it to the layers so the whole mix is covered. Add cheese on top and put it in oven for 40-60 minutes at180c circulating air.
Here is a recipe in English. I haven't tried this one but looked ok.
https://eatingeuropean.com/potato-leek-casserole/