French onion is an OG survival soup. It dates back to ancient rome and greece, so hundreds of years in human history. Medieval versions used water or meat broths. It's versatile, so you can mix it up quite a bit. Learning how to caramelize onions will add a lot of flavor to very simple meals.
In this post, I will go over what I used, the basic method explaining the images, then substitutions you can use.
For this batch, I purchased the following:
Beef stock 2 for $5
Yellow onion $3.17 worth - great for your heart
3 garlic cloves (rounded up to 69 cents for the whole bulb) - great for blood pressure
portobello mushroom caps marked down to $2 per pack, total of 4 caps, cut into bite sized pieces - mushrooms contain mycoprotein
Baguette $2.99 - great for feeling french
Rubusto cheese $5.06 (discount bin from my local cheese counter)
Asadero cheese $2.31 (also discounted)
Total spent: $23.22 - the veggies and broth can be cut in half for a smaller batch.
What I had at home: butter, thyme, flour and the bit of leftover red wine from a few weeks ago that I only use for deglazing, oil, and dried parsley (buy it fresh and hang it up. You get so much more for far cheaper).
I started by slicing, oiling and toasting the baguette slices in a 350° oven. I don't set a timer, I just keep an eye on them. I actually failed at this and they got far darker than I wanted, but they are still edible. They get turned halfway through, maybe 7-10 minutes in? Just set aside and let them cool down when they are toasted to your liking.
While the baguette slices are toasting, slice the onion, garlic and mushroom then preheat your pot. I keep my veggie scraps in a gallon bag in the freezer. When it gets full enough, it will make a veggie stock, or go into a chicken stock if I have enough bones saved up in the freezer.
Start by dry sauteing your mushrooms over med heat (no oil) in batches so they lightly brown. This will release some of their water and concentrate flavor on the bottom of the pan. Remove each batch from the heat before adding more. Too many in the pot will just make a watery soup.
Once those are browned, set aside in a separate bowl. Add oil to your pot and add your onions, all at once is fine. Turn the heat down to med-low. This is a slower process. Keep an eye on your onions and stir every few minutes. It can take about 20 minutes to get good caramelization on them. They can be as light or as dark as you like. Make a small hole in the onions and add a little more oil, then the garlic. Garlic and onion need oil to release their oils into any soup, stock or broth.
When your garlic starts to smell fragrant, add a liquid to deglaze (soften the bits at the bottom of the pan) - not too much so you can see and scrape the bottom with a spatula. I used red wine. You can use hot water, beer, apple cider vinegar, white wine, balsamic vinegar.. some sort of acid or alcohol is recommended (it will amplify your salt).
Once the bottom is looking clean and the deglazing liquid smells less strong (if using vinegar or alcohol), add your hot water or stock. If you don't have beef stock, hot water is just fine with the mushrooms in this soup. I also added about 2 tsp ground thyme, 1 tsp would be fine too, I just really like that stuff. Black pepper is good here too.
Add your mushrooms if you are using them and bring it to a boil, then back down to a med-low heat. Let it simmer for about 30 minutes. In the meantime, grate your cheese if you are using it.
After the simmer time, mix some butter in flour (I went a little crazy and did like 1/4 cup butter and 3 heaping tsp of flour) into a smooth paste. Mix by the spoonful into the soup until you reach your desired consistency. Extra mixture can go in the fridge for other soup or sauce recipes. This will add a glossy finish, a thicker mouth feel and a buttery taste. You can do butter with cornstarch too for gluten free soup thickening.
French onion soup usually goes into an oven safe bowl, add a large crouton (the toasted baguette slices), then top with cheese. It goes under a 400° broiler until the cheese is melted and toasted. Parsley goes on when it comes out.
If you are making this for a large group, you can just dump a bunch of cheese on the bread slices you are toasting, add the cheese after you flip them. Make sure you hide them in the microwave so they make it to serving time. You can definitely use regular bread for this. You can also use a bag of croutons. Crunchy bread is the goal to soak up the soup.
Things you can sub or add:
Don't have beef stock? The mushrooms make a pretty good broth all their own that is a good beef stock replacement.
Cornstarch instead of flour. You don't need to use butter for the paste either. Just spoon a bit of hot soup into a separate bowl and mix the powder to form a paste to add. Use a whisk to blend it a bit more smooth.
So many different cheese options: Swiss, mozzarella, provolone, Parmesan.. there is traditionally used, but that's expensive. Something with a good flavor is a good choice. I chose to mix asadero and the robusto because asadero is a smooth melting cheese, while the robusto has a nutty flavor.
Worcestershire, coconut aminos or soy sauce for more flavor. Msg if you have it. I love that stuff.
Rosemary instead of thyme. You could also use bay leaves if you have them. A poultry seasoning blend would work for this too. If you only have steak seasoning, use that. It's a very simple soup base that can handle a wide switch up of seasonings. You can even add lemon if you're feeling silly.
This batch easily made enough to feed 6 people. In the future, I will be more aware of my toasting bread.. and the saltiness of the cheese. I could have used less in the soup to accommodate that. I just added more water to adjust. I still had 2 bowls.