There is a place called Caldeira in Furnas, in the isle of São Miguel, Azores, with several natural holes. The volcanic fumes give out boiling water steam due to the volcanic activity of the area.
Amateur and occasional chefs take advantage of these conditions and the water temperature to cook pleasing friends, family, and tourists.
In fact, they cook for all those who are curious and travel to this area to enjoy these snacks baked without an oven.
The Furnas codfish is a must.
There are several dishes cooked underground with the help of volcanic heat. The preparation method – where it takes three to five hours to cook the codfish – is the secret to the delicate and special flavour of this dish.
Shred the soaked codfish from the day before in large pieces with no skin or bones. Peel and slice the potatoes – make sure the slices are not too thin – into a container with salt water.
Pour the olive oil into a casserole with a hermetic lid that closes with clamps. Then, lay very fine slices of onion, potato slices, codfish pieces, and tomato pulp with no skin or seeds.
Season with peppercorn and cumin or clove to taste, add lard and butter, and close the lid involving it in a burlap bag.
Bury it in the warm mud of S. Miguel volcanic holes and let it cook for an hour and a half.
Selecções do Reader’s Digest. (1984). Tesouros da Cozinha Tradicional Portuguesa. Porto, p. 70-71