2 tablespoons extra-virgin olive oil
3 tablespoons butter
1 pound button mushrooms, trimmed and halved
1 1-pound bag frozen pearl onions, defrosted, then drained on a kitchen towel to remove excess liquid
4 large garlic cloves, finely chopped
2 large carrots, peeled and thinly sliced
3 celery ribs, thinly sliced
1 teaspoon red pepper flakes, 1/3 palm full
Salt and black pepper
1 24-ounce log prepared plain or flavored polenta (on the refrigerator aisle)
1 1-pound ball fresh mozzarella cheese
3 tablespoons all-purpose flour
1 cup dry white wine
1 quart chicken stock
½ cup heavy cream or half-and-half
2 cooked rotisserie chickens
1 pint red grape tomatoes
1 10-ounce box frozen peas
1½ cups fresh basil, about 25 leaves, coarsely chopped or torn
¾ cup fresh flat-leaf parsley leaves, about 3 generous handfuls, chopped
1 cup grated Parmigiano-Reggiano cheese, 3 overflowing handfuls
1. Preheat the broiler. Place rack at the center position or drop the lower or upper broiler pans as far from the heat source as possible.
2. Preheat a large pot over medium-high heat with the extra-virgin olive oil, 2 times around the pan. Add the butter and, once it melts, add the mushrooms and cook for 4 to 5 minutes to give them a little color. Add the pearl onions, garlic, carrots, celery, red pepper flakes and a little salt and pepper. Cook 5 minutes longer, stirring occasionally.
3. While the veggies cook, slice the polenta log into ¼-inch-thick disks. One log should yield 20 to 22 disks. Have the ball of mozzarella, then slice each half into ¼-inch-thick half moons and reserve alongside the polenta disks.
4. Sprinkle the flour into the veggies and stir to combine, then continue to cook for another minute or two. Add the white wine, scraping up any bits on the bottom of the pot with a wooden spoon. Add the chicken stock and cream, and bring up to a bubble, then simmer for 10 minutes.
5. Remove all the meat from the rotisserie chickens, tearing it into large bite-size pieces and discarding the skin. Add the chicken meat to the simmering sauce as you break it up. Once all the meat is in the pot, add the tomatoes and peas, and cook for another 2 minutes. Add the basil and parsley; taste to adjust the seasoning. Transfer the mixture to a large oval or rectangular baking dish, casserole or lasagna pan. (Disposable pans are fine too, but buy two and double them up for sturdiness and to keep the bottom of the pot pie from scorching.)
6. Shingle the polenta disks and the mozzarella half moons over the top of the chicken and vegetables, distributing the cheese evenly among the polenta. Sprinkle the top of the assembled dish with the grated cheese and transfer to the broiler several inches from the heat. Broil until the polenta is warm and the cheeses have browned.