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.