Make the polenta and keep it warm. Unwind the pancetta into a long strip and cut crosswise into 1/4-inch wide pieces. Heat together the pancetta and the 1 tablespoon olive oil in a skillet over medium heat. Cook slowly until well-browned and crisp. Tilt the pan to collect the fat in a little pool against the side and scrape the pancetta into the fat. Cook for another minute to make sure the pancetta is very crisp. Remove with a slotted spoon to paper towels to drain. Set the pancetta aside.
There should be about 2 tablespoons fat remaining in the pan. If not, add a little olive oil. Turn the heat to medium-high and heat until hot. Add the garlic and saute briefly until light brown. Add the thyme, stir, add the stock, and bring to a boil. Cook until reduced by about half. Add the broccoli rabe, season with salt and pepper, toss well, cover, reduce the heat to low, and cook until tender, about 5 minutes.
Pour the polenta into a warm serving dish or bowl and pour the vegetables over it. Sprinkle with the reserved pancetta.
Combine the stock and cream in a heavy saucepan and bring to a simmer. Add the nutmeg, salt, and pepper. Whisk in the polenta and semolina, and cook over very low heat, whisking regularly, until the grains are soft, about 8 minutes. Whisk in the cheeses. Serve immediately or reserve. To encourage polenta to come cleanly out of the pan, put the pan over medium heat. Run a spatula or wooden spoon around the sides of the pan to clean off the polenta. Do not stir, but wait and watch for a few seconds until a large bubble begins to form and push the polenta upward. Pour immediately into a warm dish. The polenta can be made ahead and reheated: add 1/4 to 1/2 cup water or stock, cover the dish, and reheat in the microwave or over low heat. Whisk well before serving.
Recipe courtesy of Michael Chiarello, from The Tra Vigne Cookbook Chronicle (1999)