Peel the potatoes and clean the green beans without removing the tips. Cook separately in boiling salted water the peeled potatoes and the green beans. Once cooked, drain and put in a bowl after removing the tips of the green beans.
Cook the shelled beans. Drain and put in the bowl with the potatoes and the green beans.
Slice the onion and fry in butter. When it is lightly coloured take off the fire.
With a wooden spoon crush the vegetables coarsely and pour in the pan with the onion. Stir the whole over low heat for 5 minutes.
Cut the Casera cheese into small cubes. Add to the vegetables in the pan the remaining butter, the Casera cheese cut in pieces, the grated cheese, salt and pepper. Serve before the cheese sets.