Spray bowl of slow-cooker with nonstick spray to make clean up easier.
Add sliced onions and remaining ingredients. There's no need to strip the leaves from thyme. Simply place the sprigs on top and remove them before eating the onions.
Cover. Cook on medium/low for 24 hours or on high for approximately 8 to 10 hours until the onions are a deep caramel color. Stir once or twice toward the end of the cooking time.
Use on sandwiches, salads, omelettes, soups. Serve as a side dish with meat. Chop fine and mix with butter for a delicious compound butter that is outstanding atop steaks. Use a garnish for dried beans (navy, pinto, blackeye peas, etc.). I'm making French Onion Soup with these babies!
Freeze in small containers. Take out only what you think you will use up in a few days.