Put a clay casserole on the fire with the broth and butter. When boiling, add the trotters (split in half) and simmer, leave it for a while to soften.
We will have the mushrooms soaking for at least an hour and we will take them to the pan with a little water in which we will have had them.
Leave half an hour with little fire, waiting for the juice to reduce and then pour the Porto.
Continue to simmer, allowing to reduce the broth.