Raise the heat to medium-high, and place the Brussels sprouts cut-side down in the bacon fat. Cook undisturbed, about 2 minutes, until they begin to crisp and brown. Stir in the sliced onion, and cook, stirring occasionally, until the onion is translucent, about 5 minutes. Stir in the broth, vermouth, and dried cranberries, and scrape up any browned bits from the bottom of the skillet. Bring to a simmer, then cover, reduce heat to medium, and cook until the Brussels sprouts are tender, about 10 minutes.