Season the fish with salt and pepper and place in the refrigerator until ready to use.

Heat the olive oil in a large, heavy skillet, add the leek and garlic, and sweat over low heat until the leek is very soft, about 20 minutes. Add the paprika and cayenne and stir with a wooden spoon for about a minute. Add the tomato paste and stir for another minute. Pour in 1/2 cup/120 ml of the wine and the water. Bring to a gentle boil, reduce the heat to low, and simmer, covered, until the sauce is thick and dark, about 15 minutes. Season with salt and pepper.

Place the fish over the leeks in the skillet. Add the remaining 1/2 cup/120 ml wine, cover the skillet, and simmer until the fish is flaky and tender, another 15 minutes or so, depending on the size of the fish. Remove from the heat, let stand for about 5 minutes, and serve.