Boil onions in a little salted water, till done.
Boil the beans separately.
Melt 1 level dessertspoon butter in a pan and add 1 good dessertspoon flour, stirring well till a paste forms then gradually add 3/4 cup water in which the onions were cooked.
If there is insufficient onion water make up the quantity with water from the beans.
Boil, stirring often, till a sauce forms, seasoning to taste with salt and pepper.
Pour the sauce into a shallow fireproof dish of medium size.
Stand the boiled onions in the dish and arrange the beans between them.
Mix together cheese and breadcrumbs and sprinkle over the dish, dotting here and there with little dabs of butter.
Bake till a golden brown at400°F.Gas6.