Amid a tangle of narrow residential streets behind the seafront at Foz is a little stone house that many believe holds the most extraordinary modern restaurant in Porto, even the whole country. Chef Pedro Lemos won his first Michelin star shortly after opening in 2014. Menus are of three, five or seven courses. What's on them depends on what the fishing boats have brought in that morning, or what's in season in Lemos' own vegetable garden, but they will include treats like pigeon with foie gras and fennel, sea bass with turnip and chestnut, banana with lavender and Madeira wine.   All this is served in two intimate dining rooms decorated in warm gold and blue tones, and a rooftop terrace looking towards the mouth of the Douro.