Prepare fish by cutting close, shallow slits into the skin. Cut leeks in half lengthwise, clean well and cut into ⅛-inch slices.Place leeks and butter into a small pot and season with salt. Cover and turn heat on low. Let leeks cook until very soft, stirring occasionally, then add cream. Reduce cream over medium heat until thickened. Set aside and keep warm.Put into a saucepan the wine, peppercorns, cardamom, thyme, garlic and 1 tablespoon sugar. Reduce over medium-high heat until it coats the back of a spoon. Season with salt, strain and set aside.Put dried fruit, capers, wine vinegar and 1 tablespoon sugar into a sauce pot. Cook over medium heat until thick.Season whitefish. Heat oil in a large frying pan over medium-high flame until the oil just begins to shimmer and smoke. Carefully place 2 filets at a time into the oil, skin side down. Cook almost all the way through—you will know it when you see it by the change in color. Flip filets and cook 30 seconds more, then place onto a warm plate with a napkin.To plate, spoon leeks evenly onto 4 plates. Place fish onto the leeks. Shape a quenelle of the chutney for the top of the plate and drizzle with wine sauce.