If pancetta is unavailable, you can substitute bacon, cut it into 1/2-inch (12-mm) strips. It may take a little longer to crisp than pancetta, so add it to the Brussels sprouts after they've been roasting for 10 minutes and continue to cook until everything is crispy, 20 to 25 minutes more. Keep in mind that bacon can be quite salty, so you may want to reduce the amount of salt you use for seasoning the Brussels sprouts.