Place the anchovies, covered with plenty of coarse salt, into a container and let in the fridge, covered, until the next day.
Wash the anchovies and the container to remove the salt.
Place the anchovies into the container again, cover with water and let this way for 1 hour at least to prevent an excess of salt.
Meanwhile, fillet the garlic and fry lightly in extra virgin olive oil.
Chop the sweet peppers, add them to the oil and confit at medium heat.
Drain the anchovies very well and place them on a big pan.
Cover with the garlic and peppers.
Pour the tomato and onions sauce covering the fish. Tha sauce must be thick because the anchovies will loose water.
Bake for 5 minutes (200ºC)