Slow-Cooker Sweet Onion Jam with Pancetta

Stir together the onions, pancetta, vinegar, brown sugar, thyme, pepper, and salt in a 6-quart slow cooker. Cover and cook on LOW until the onions are very tender, about 7 hours. Uncover and stir well. Increase the heat to HIGH, and cook, uncovered, until the desired consistency, about 1 hour. Skim the fat, and discard. Cool to room temperature, about 1 hour. Serve at room temperature or cold.