Preheat the oven to 400°F.
In a large skillet over medium heat, sauté the pancetta, shallot, and garlic for about 5 minutes (the pancetta will release some fat, so you don’t really need any additional oil).
Chop the reserved inside parts of the Brussels sprouts, add to the pan, and cook for 5 to 6 minutes more.
Remove from the heat, season with pepper, and carefully spoon the mixture into the Brussels sprout shells.
Place the stuffed Brussels sprouts on a baking sheet, cook in the oven for 10 to 15 minutes, until tender, and serve.