potluck: french onion soup (no beef stock)

We hosted a potluck at our suite to celebrate the end of the semester and to send off a friend who will be studying abroad in Amsterdam. My friend Anna and I teamed up to make some hearty french onion soup. It was definitely in the stars for us because 1) we had a bag of onions leftover, and we needed to clear our fridge before winter break and 2) Anna received a slow cooker, and we were eager to try it out. So, on a cold winter day, what better way to put a slow cooker and a bag of onions to use than to make some hearty french onion soup!
While beef stock is usually an integral part of french onion soup, neither Anna nor I eat beef, so we substituted it with chicken and vegetable stock. We left out the cheese because we didn't have heat-safe bowls to broil the cheese with. Regardless - topped with a thick slice of toasted french bread, this soup is d-i-v-i-n-e.

Doranna's slow cooker french onion soup (no beef stock; cheese optional)
4 medium yellow onions, sliced French-style
3 cups chicken stock
3 cups vegetable stock
2 Tbs all-purpose flour
3 Tbs butter/oil (we used 1 Tbs olive oil + 2 Tbs butter)
Ground pepper, thyme, to taste

Optional: gruyere cheese, grated
French bread, to serve with soup

1. Slice the onions into strips.
2. In a pan, heat the oil and the butter until it melts together.
3. Add the onions to the pan and cook on Med-High until golden brown and caramelized (~45 minutes). If there are brown caramelized bits stuck to the bottom of the pan, pour in a few splashes of chicken or vegetable stock to deglaze it.
4. In a slow cooker, pour in the chicken and veggie stock. Add flour, ground pepper and thyme to the stock, and mix until the flour has dissolved. Add in the caramelized onions, making sure to scrape all the caramelized bits off the pan and into the slow cooker.
5. Turn the slow cooker on HIGH, and let the soup cook for 2-3 hours, until the soup is bubbling, the onions have broken down, and everything has melded together.
6. Optional: Divide the soup into individual heat-safe bowls. Add a slice of french bread and a handful of grated gruyere cheese on top of the soup. Broil in the oven for 3-5 minutes, or until cheese and bread are golden brown.
7. Alternatively, you can do it like we did, and simply serve it with a slice of french bread.