Put the butter in a 12-inch skillet over medium heat. When the butter has melted, add the onions and Sauté until they turn a rich golden color, about 5 minutes.
Add the bacon and continue cooking until it becomes lightly browned but not crisp. Add the radicchio and endive, season with salt and pepper and stir until the vegetables are coated with the butter. Lower the heat to low, cover the pan and cook, stirring occasionally, until the endive and radicchio has wilted completely and achieved an almost creamy consistency, 15 to 20 minutes.
Fill a pot for the pasta with about 6quarts of water, cover, and place over high heat.
Uncover the pan, raise the heat to medium high and let any liquid the vegetables have released evaporate. Add the cream and cook until it has reduced by half. Stir in the parsley and remove the pan from the heat.
Add 2tablespoons salt to the boiling pasta water, add the penne, and stir well. Cook until al dente. When the pasta is done, drain well, toss with the sauce and the grated Parmigiano-Reggiano. Serve at once.