Creamy Baked Salt Cod - boneless baccala

Method

• To remove the salt from the salt cod, put it in a large, deep container that fits in your sink, under the faucet.
• Run fresh cold water over the fish, filling the container completely so water is spilling over the brim.
• Keep a slow, steady drip of fresh water going as you soak the baccala for at least 12 hours, up to a couple of days.
• Occasionally drain the water and refresh (which you can do whenever you need the sink).
• If you cant keep the drip going, change the water every 4 hours.
• To decide when baccala has been soaked sufficiently, lift the fish out of the water, press a finger against it at a thick part, and touch it to the tongue.
• If its palatably salty, it is ready to be cooked.
• Drain the baccala, pat dry, and cook within a day or so; meanwhile, store it in the refrigerator, well wrapped.
• Cut the baccala into chunks about 3 inches square, and dredge on all sides in flour.
• Put the butter and olive oil in the saucepan, and set over medium heat.
• When the butter is foaming, lay in a batch of floured codfish chunks in one layer, not crowded.
• Cook and color the underside for several minutes, turn the chunks, and crisp and color the other sides.
• When lightly browned all over, remove to a platter.
• Fry the remaining chunks the same way.
• Dump the onion slices into the pan, and toss well in the remaining fat.
• As the onions start to sizzle and wilt, pour in 1/2 cup water, and stir and scrape up the browned bits on the pan bottom.
• Cook the onions, stirring frequently, until wilted and translucent, 8 to 10 minutes.
• Meanwhile, heat the milk in a separate pan, almost to a simmer.
• Lay the baccala chunks on top of the caramelized onions, nestling all the chunks in one layer.
• Pour in any juices from the fish platter, and enough hot milk to cover the fish completely.
• Over medium heat, bring the milk to a gentle bubbling simmer.
• Set the cover slightly ajar, and simmer the baccala for about an hour and a half, until the fish chunks break apart when stirred.
• Uncover the pan, and maintain the slow simmer to gradually reduce the milk (which by now has curdled and separatedno cause for concern).
• Stir the fish occasionally, and break up the flakes into smaller pieces.
• As the moisture evaporates, lower the heat and scrape up any crust on the pan bottom, to avoid burning.
• Cook uncovered, slowly, for 2 to 2 1/2 hours, until the baccala and milk have melded into a thick sauce, about half the original volume.
• (If you need to shorten the cooking time, boil the milk over higher heat, but be sure to stir the baccala and scrape the saucepan frequently.)
• When it is fully cooked and thickened in the saucepan, pour the hot baccala into the baking dish and spread it in an even layer.
• Heat the oven to 350 , and set a rack in the center.
• Sprinkle the grated Grana Padano or Parmigiano-Reggiano over the top of the baccala, and bake for about an hour, or until the top is crusty and browned.
• Bake slices of firm polenta, topped with grated cheese, during the last 15 or 20 minutes that the baccala is in the oven.
• To serve, put a slice or more of crisp polenta in a plate, and spoon some hot baccala alongside.