**UPDATE: Yes, you CAN use raw milk. It's more temperamental though. If after the wait time the yogurt still isn't firm, turn the slow cooker back on to "warm" and let it sit another 4 hours or until thickened. Raw milk yogurt often tends to be clumpier.
**You don't have to use the slow cooker method. For a quicker method simply heat the milk in a large stock pot over low to medium heat. Just be sure to stir it regularly, especially as it gets hotter, to prevent the milk from scorching. Then follow the rest of the instructions as written.