Tear off any broccoli leaves and trim the bottoms of the stems. Cut the florets just above where they join the large stem, and then cut each floret through its stem (but not the buds) so that each piece is about 1/4 inch thick at the stem end. Using a vegetable peeler or paring knife, peel the tough outer skin from the large stem, removing as little flesh as possible. Cut the stem into baton-shaped pieces about 1/4 inch wide and 2 inches long.

Heat the oil in a 12-inch skillet over medium heat. Add the pancetta and cook until it's translucent and just starting to render its fat, about 2 minutes. Add the broccoli, garlic, salt, and chile flakes; stir to combine. Reduce the heat to medium low and cook uncovered, stirring every 5 to 10 minutes, until the broccoli is tender and slightly browned, about 45 minutes total. Taste and add more salt, if necessary. Let cool briefly and serve.