For the creamy polenta: In a heavy-based saucepan, combine the cream and milk and heat over medium-high heat just until small bubbles begin to appear on the surface. Add the salt, and whisk the cream and milk until quite frothy. (I don't have a scientific explanation as to why this whisking step is important; but I know from experience that when I don't do it, my polenta just doesn't seem as delicious as usual. Since this initial whisk is easy and takes practically no time, I recommend you do it, too.)
Add the polenta and continue to whisk the mixture as it comes to a boil. Continue whisking for an additional 3 minutes. Reduce the heat to very low, cover the pan, and cook the polenta, stirring every 5 minutes or so (switch to a wooden spoon), until the cornmeal is completely cooked and quite tender, 2 1/2 to 3 1/2 hours. It may seem very thin initially, but it will gradually thicken. As the polenta cooks, a skin will form on the bottom and sides of pan (if you are not using a nonstick pan), which is proper and which gives the polenta a slightly toasty flavor.
For the fricassee of truffled mushrooms: In a large saute pan, heat the oil over medium heat. Add the shallots and cook, stirring, until the shallots just begin to color on their edges. Add the mushrooms and crushed red pepper to taste and cook until the liquid is released. Add the chicken reduction, bring to a boil, reduce to a bubbling simmer and cook until the liquid is reduced by half. (You can prepare the mushrooms ahead up to this point; reheat them over medium-high heat just before serving.)
Just before serving, stir in the butter, grana padano or Parmigiano-Reggiano and chives if using. The polenta should pour from the spoon as you serve it and will thicken as it cools. If necessary, you can thin the polenta with a little milk just before serving. Divide the polenta among heated bowls or plates.
Just before serving, reheat the mushrooms if necessary. Toss the mushrooms with the chives and preserved truffles. Spoon some mushrooms and some of the cooking juices over each serving of polenta.
Preheat the oven to 425 degrees F. Rinse the chicken bones and pat them dry. Spread them out in single layer with a little room between the bones on one large or a couple smaller sheet pans. Roast until they are golden brown, flipping and turning the bones every 15 minutes or so, about 1 hour.
In a large stockpot, heat the olive oil over medium heat. Add the celery, carrots, garlic and onions, and cook, stirring occasionally, until the vegetables are well browned, about 20 minutes. Add the wine, tomatoes and bones to the stockpot. Add enough water to cover everything by about 2 inches (about 6 quarts). Cook over medium heat (you want a gentle simmer, not a boil) until the chicken is falling off of the bone and the stock has a full flavor, about 1 1/2 hours.
Remove the chicken and strain the broth several times through a chinois or other fine strainer. If you want to make and use the reduction right away, spoon off any visible fat floating on top of the stock. Otherwise, chill the stock until the fat solidifies on top and then scrape off and discard most of it.
Pour the defatted stock into a saucepan and bring to a boil over high heat, and then reduce the heat slightly so the stock is not boiling so furiously. As the stock simmers, some of it will remain on the sides of the saucepan; use a spoon or ladle to pour some of the stock over this to deglaze it. (This will further increase the intensity of the flavor.) Continue simmering until the stock has darkened and reduced to about 1 quart. The time this will take will vary, but it will likely take at least 20 to 30 minutes. Use right away, refrigerate for up to three days or freeze. Makes about 1 quart.