First of all you need to be prepared for this soup. You will be crying your eyes out cutting up the onions and then your house will smell like caramelized onions (things could be worse). Is this like real onion soup cooked on the stove - no - but it's pretty darn close.
Slow Cooker Onion Soup (Adapted from Cooking Light)
4 T butter (1/2 stick)
6 thyme sprigs
1 bay leaf
5 lbs of sweet onions, sliced vertically (about 16 cups)
2 T sugar
6 c beef stock (homemade)
2 T balsamic vinegar
sliced baguette toasted
1 1/4 c shredded Gruyere or Fontina cheese
Place butter, thyme, bay leaf in a slow cooker. Add layers of onions and sprinkle some salt and sugar in between layers. Cover and cook for 8 hours on HIGH. Add stock, pepper, and vinegar. Cover and cook 30 minutes on HIGH. Remove bay leaf and thyme sprigs.
Toast baguette slices under broiler. Place soup in ramekins or ovenproof bowls. Top with toast and cheese and place under broiler until cheese melts and browns slightly.
I must confess I did not put my soup under the broiler. I just toasted regular bread in the toaster and broke it into pieces and then sprinkled some cheese on top. It was still delicious. Sometimes you just need to make due with what you have on hand.
Since my stock was frozen. I defrosted it in the microwave and heated it until it was a little warm. This gave me a little advantage in that I didn't need to heat it for the full 30 minutes in the slow cooker. You might need to add a little extra balsamic vinegar depending on how sweet the onions are.
What's up with all this soup I'm making lately?