I will try to explain this recipe as the fishermen performed the Tarragona coast, specifically in Las Casas de Alcanar.
The potatoes are peeled in disks 2 or 3 millimeters thick. They are distributed in a large skillet and some deep (can also be mud), in which we will put a bot of "the picada". We cover with fish stock.
When the potatoes are almost cooked add the fish over we will have prepared and cleaned. It is not necessary that covers it by the broth. The final cooking will take about 12 minutes and when the fish is half cooked should be rotated. A 10 minutes to finish cook add the rest of "the picada".
You will see that with these ingredients is a delicious suquet. The fish is indicated as an example. You can use any strong fish meat (Rap, scorpionfish, sets sail, sea bass etc)
To make the "Picada"
We will put in a mortar the garlic, tomato (blanched and peeled) and parsley and crush all, adding a ½ liter of broth, until a fairly thick sauce.