The beauty of this French onion soup recipe is twofold – it’s dead simple, and it’s flexible. I actually made this and wrote it up over a year ago, but never published it, so I had the chance to make it again last week (#quarantinecooking) with a slightly different method to see if it was as good as I remembered. It is! It was partially inspired by this recipe, but I made a number of changes.
Having now made this in the slow cooker several times, I’ll never make French onion soup the traditional way again – all that time and work caramelizing onions on the stove is just not worth it. If you take the looooong slow-cooker way, you’ll be rewarded with ultra-caramelized onions and an incredibly deep and rich flavor – not to mention a delicate onion perfume throughout your house. If you’re not into onion perfume, or perhaps are looking to start this in the morning and have it ready for dinner later that night, then you’ll still be rewarded with a hearty and delicious soup with the faster slow-cooker way.
This recipe is a great base from which to start and get even more creative. I’ve made it vegetarian (subbing vegetable broth) and it was just as good, and it could easily go vegan by just swapping oil for butter. Herbs and spices could certainly be added, like some fresh or dried thyme, or warming spices like star anise or Chinese 5-spice powder. To be honest, though, I kind of dig highlighting the pure, unadulterated flavor of the humble onion.
I also want to talk about cutting onions. No, not crying – literally, cutting onions. I’ve never in my life sliced onions ‘against the grain’ – aka through the equator. It’s never even something I’ve thought about before, no matter how I need the final onion (minced, chopped, sliced) I always start with halving the onion through the root. However, when I was reading various French onion soup recipes, one of them specified to slice the onions across the grain and then cut in half – so i thought, why not experiment? I also remembered reading in Cook’s Illustrated that cutting onions with the grain results in a milder flavor with a texture that breaks down easier, while cutting against the grain results in a more aggressive flavor and texture that holds its shape more. For my most recent batch of soup, I simply did half the onions my normal way and half the other way – slicing through the equator – to see if I could tell the difference. Bottom line? Given they cooked for so long and were part of a soup, the type of cut made no difference in flavor in this application, but the texture difference was discernible. The onions cut against the grain held their shape more so than the other ones, and I actually didn’t like that as much. So as for me and my house, we will continue to slice onions the way we always have!
If you’re looking for another easy soup recipe, try this cauliflower soup!
World’s Easiest French Onion Soup
I've made this soup with two different slow-cooking methods, which really just vary depending on how much time you have and what you're in the mood for; you'll also see notes for ingredient options as I've made it both 'regular' and vegetarian. I said it was easy and flexible!
Ingredients
- 3.5 lbs onions, sliced, with those slices halved this equates to 4 large onions; can use yellow, sweet, red or a mix of all (don't recommend using only red)
- 3 Tbsp unsalted butter use oil to make vegan
- 1 Tbsp brown sugar
- 6 c beef broth or vegetable
- 3 Tbsp balsamic vinegar, red wine or Worcestershire sauce use whatever you have in whatever combination you fancy – I recommend 1 tsp of Worcestershire sauce and the remainder either vinegar or red wine if you have some open; this helps give an umami boost to the soup
- 1 Tbsp sherry, brandy or cognac optional, but adds a classic yet subtle taste
- black pepper
- salt to taste
Instructions
Overnight Method
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The night before you want to eat, slice the onions (see blog post above for guidance on which way to slice), and then cut those slices in half so that they'll easily fit on a spoon when you're eating.
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Add onions and butter or oil to a large slow cooker, and set on low heat for 8-10 hours (depending on how long you'll be asleep – I like to start it before bed, and let it go until right before I wake up – my model shifts to 'keep warm' when the time is up). I don't set it to beyond 10 hours because I want to make sure I can check on things when I wake up.
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Wake up to the smell of delicious caramelizing onions! They should be golden brown and have released a lot of liquid at this point. Stir the onions around, scraping down the sides if necessary. It's possible some onions around the edges may have gotten very brown but that just means more flavor 🙂 At this point, if you have any interest in saving some caramelized onions for future recipes, remove some now – I removed about a cup and a half, so I still had plenty left for the soup.
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Since I was 1) working from home, 2) loved the smell and 3) didn't need to eat it until dinner, I let the onions continue to cook on low all day. Their color and flavor deepened even more over the next six hours.
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Around 2pm, I added the broth and the 3 Tbsp of additional flavor (this time, balsamic vinegar and Worcestershire sauce) – don't add the brandy/cognac/sherry yet, if using, or the salt/pepper – and set back on low for 4 hours.
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Right before serving, I stirred in the cognac and some freshly ground black pepper. After tasting, I decided it didn't need additional salt as the vegetable broth I used was fairly salty.
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It's traditional to spoon the soup into ovenproof bowls, top with crusty bread covered in gruyere or swiss cheese and then melt it under a broiler – and I mean, that's delicious and you should definitely do that. However, the soup also tastes amazing without that, or with just some leftover pizza crust and parmesan cheese, if that's all you happen to have on hand at the moment…just saying 😉
One-Day Method
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Place the sliced onions and butter or oil in the slow cooker in the morning, and set on low for as long as you'll be gone – 6-8 hours.
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Return home, welcomed by the smell of delicious caramelizing onions. Crank up the heat to high, add your broth, 3 Tbsp flavorings and 1 Tbsp alcohol (if using), and let it cook for at least 1 more hour, ideally 2, so the flavors can meld together.
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Season with black pepper and salt, if needed. Serving suggestions are the same as above.
Michael Pecoraro says
It won’t let me “like” this post because i don’t have a Word Press account. I love French Onion Soup and would love to try this out. Looks awesome.
Kristen says
Love the remarks about slicing the onions in two ways… I would never have thought it would make any difference. Haha good idea about conducting your own experiment 🙂 Nice post! :_)