Rich, warm, and super savory, this French onion soup contains beef stock and caramelized onions, topped with toasted bread and melted cheese - a warming favorite for chilly days!
Peel and thinly slice the onions. I do this by slicing off the root and stem ends of the onion. Chop it in half (from top to bottom), then place the onion halves cut-side down and slice (make cuts about ¼-inch apart).
Heat the olive oil in a large deep-bottomed soup pot/Dutch oven over medium-high heat. Once hot, add the onions and cook, stirring often, for around 10 minutes until they’re beginning to brown.If you notice pieces burning rather than just browning, reduce the heat slightly. Make sure to stir well to lift up browned bits from the bottom of your pot each time you stir. You can lightly deglaze the pan with a splash of your stock or wine as needed at the end of the process, too (before adding flour).
Meanwhile, chop one of the garlic cloves and add it to the onions along with the sugar and thyme.
Stir well, reduce the heat to medium, and cook for 30 minutes. Stir infrequently to begin (every 4-5 minutes) and more so towards the end (every 1-2 minutes), as they’re more likely to burn once reduced/caramelized.Adjust the time if needed until you achieve soft and slightly sweet onions with a rich golden brown color. Feel free to move on to the next step earlier if you like the taste when the onions are slightly less caramelized.
Make the broth
Add the flour to the pan and stir well to combine, allowing it to cook for 2 minutes. Add the wine (use it to deglaze the pan and scrape up any browned bits from the bottom of the pan) and beef/veggie stock, stirring well, and bring the mixture to a rolling boil.
Skim and foam from the surface of the soup, then lower the heat to a gentle simmer, cover with a lid, and allow it to cook for a further 40-45 minutes.
Assemble and serve
Preheat the oven grill. Then, toast the bread slices under it (usually 5-8 minutes total).
Pour the soup into oven-safe bowls/ramekins (wide enough for your bread pieces), filling them ¾ way. Then place a piece of the toast in each bowl and top with freshly grated cheese until you can’t see the soup below.If you don't have oven-safe bowls, make cheesy garlic bread to serve with the French onion soup instead. Simply spread toasted bread on a baking sheet, add cheese, and broil before adding to the soup.
Broil the ramekins for several minutes until the cheese has melted and begind to bubble. It's best to broil them around 6-inches/15cm away from the heat source. Serve piping hot!
How to store
To make ahead: Prepare soup without cheesy bread topping up to 4 days in advance. Store in the fridge. Then reheat when needed and add the topping (the flavor will develop in the fridge and taste even better!).Freeze: Freeze the cooled soup (without bread/cheese topping) in airtight containers or Ziplock bags (portioned, with headspace) for up to 3 months. Thaw in the refrigerator before reheating or speed up the process in a hot water bath.Reheat: Gently reheat the soup in the microwave or on the stovetop, adding extra broth or water if needed.
Video
Notes
Don’t over-brown the onions: or you may end up with an overly bitter soup.Avoid over-broiling the cheese: aim for golden and lightly bubbling to keep it gooey and melty. Over-browning it will make it crispy and miss out on the gooey texture.Cut the onions uniformly: that way, they’ll caramelize evenly too. Using a mandoline (carefully) to slice the onions can help for consistent results.Adjust the amount of sugar: I like to add "just" enough for a very subtle sweetness. However, feel free to adjust the amount to your taste.Don’t rush the soup: possibly the most crucial tip of all. This French onion soup is all about the rich flavor from the slowly caramelized onions, so don’t try any shortcuts!