Peel the porcini mushrooms, cut into slices.
Peel the onion and cut into half rings, defrost the beans
... In a pan with vegetable oil, fry the beans and onions, cook for 3-5 minutes, stirring occasionally. Add 1/3 cup water and simmer until the beans are soft.
Add mushrooms and salt, cook for 5-7 minutes.
Finally add butter and stir.
Put on a platter and serve.