French Onion Soup x French Dip

Lunch | French

Prep time: 20 min Cook time: 45 min Servings: 4

The classic French dip is thinly sliced beef on a roll served with a cup of jus for dipping, while French onion soup is deeply caramelised onions in a rich beef broth finished with a thick cap of melted Gruyère. This dish takes both ideas and puts them on the same plate: the soup, bubbling with cheese on top, and a hot baguette packed with seared ribeye, Swiss cheese and those same sweet caramelised onions to dip straight into it. It’s a lot but it’s very tasty.

The key to making this work is not rushing the onions. They need a full 15 minutes over medium heat, stirred regularly, until they collapse into a deep golden, sweet mass. That caramelisation is what gives the soup its body and the sandwich its backbone. The brandy goes in next to deglaze the pan and lift all that flavour into the stock. Once the soup is done I strain it into ovenproof bowls, keep the onions back for the sandwich, top with Gruyère and blast under oven heat until bubbling. The beef is cooked fast and hot in tallow, layered with the reserved onions and Swiss cheese, then tucked into the baguette.

Ingredient Notes

Brown onions: Brown onions are the right choice here because of their higher sugar content, which means they caramelise more deeply than white or red onions and develop a sweeter, more complex flavour over time. Don’t rush them. Fifteen minutes of cooking with regular stirring is what transforms them from sharp and pungent to soft, golden, and genuinely sweet.

Gruyère: Gruyère is the classic cheese for French onion soup because it has a nutty, slightly salty depth of flavour and melts beautifully under oven heat without becoming greasy or breaking. I grate it freshly rather than buying pre-grated as it melts more evenly and gives better coverage. Emmental or Comté work as substitutes and have a similar character. Avoid cheddar here as it has a sharpness that fights the sweetness of the caramelised onions.

Beef tallow: It’s rendered beef fat, available from butchers and some supermarkets. If you can’t find it, you can trim the fat from the ribeye, render it down in the pan for a minute or two before adding the beef, then proceed as normal. Lard or clarified butter are also reasonable substitutes at this temperature. If you can’t get tallow, you can use a neutral flavoured oil instead.

Equipment

Chopping board
Chef’s knife
Large saucepan
Wooden spoon or spatula
Sieve
Ladle
4 ovenproof bowls
Oven tray
Cast iron flat plate or heavy-based frying pan
2 metal spatulas or bench scrapers
Box grater

Ingredients

1kg brown onions, thinly sliced
25ml olive oil
50g unsalted butter
sea salt, to season
50ml brandy
1 tbsp plain flour
2 bay leaves
6 dashes Worcestershire sauce
4 dashes Maggi seasoning
500ml (2 cups) beef stock
2 baguettes
150g Gruyère cheese, grated
30g beef tallow
800g ribeye off the bone (or sirloin or rump), thinly sliced
150g Swiss cheese slices

Directions

Make the soup
Place the butter and the oil in a large saucepan over medium-high heat. When the butter is melted, add the onions and season with a pinch of salt.
Stir well and reduce the heat to medium. Cook the onions for 15 minutes, stirring often, until a deep golden colour.
Pour in the brandy and cook for 1 minute, to cook off the alcohol. Sprinkle over the flour and stir through, then add the bay leaves, Worcestershire and Maggi seasoning.
Pour in the stock and bring to a simmer. Cook for 10 minutes, then remove from the heat.
Divide soup and baguette
Pass the soup through a sieve and set the onions aside (for the sandwich), remove the bay leaves.
Preheat the oven to 220°C (430°F).
Ladle the soup into 4 oven-proof bowls.
Sprinkle the soups with the gruyere cheese and place on an oven tray.
Place the soups in the oven for 2-3 minutes, until the cheese has melted and is bubbling.
Slice the baguette into 4 and halve horizontally without slicing the whole way through.
Cook beef and assemble
Heat the tallow on a cast iron flat plate over high heat. Place 1 portion of the beef on the plate and season with some salt.
Cook the beef for 1-2 minutes, turning to brown on both sides. Push the beef into a mound the length and width of a baguette portion opened up.
Top with ¼ of the onions then ¼ of the cheese slices. Place the baguette, cut side open, down on top of the cheese.
Using 2 metal spatulas or bench scrapers, lift under the beef invert baguette into your hand then straight onto a serving plate and press to close.
Repeat with the remaining beef and baguette.
Serve the baguettes with the soup and dip the sandwich into the soup and enjoy!

Recipe notes

Chef Tips

Don’t rush the onions

High heat at the very start is fine to get things moving, but once you reduce to medium you need patience. Stir the onions regularly and let them break down over the full 15 minutes. The deeper the colour and the softer the texture, the better both the soup and the sandwich filling will be. If you try to speed this up with high heat throughout, you risk burning the sugars and getting a bitter result rather than a sweet one.

Keep the pan ripping hot for the beef

The beef needs to go into a very hot pan in a single layer so it sears rather than steams. Overcrowding drops the temperature and you’ll get grey, stewed meat instead of a proper crust. Cook in batches if needed, and once the beef is seared push it quickly into the shape of your baguette before it loses heat. You’re working fast at this stage so have the onions, cheese and baguette ready to go before the beef hits the pan.

Deglaze properly with the brandy

When the brandy goes in, make sure the heat is still high and let it cook for a full minute before moving on. You want the alcohol to burn off completely and the liquid to reduce right down. This is also the moment all those sticky caramelised bits on the bottom of the pan get lifted and dissolved back into the onions. That’s concentrated flavour you don’t want to leave behind.

Cook out the flour before adding stock

After you sprinkle in the flour, stir it through and give it a full minute in the pan before pouring in the stock. Raw flour has a starchy, slightly bitter edge that needs heat to cook out. That brief time in the hot onion fat coats the flour granules and eliminates any pasty taste, so the finished soup has a clean, well-rounded base. Don’t rush this step or you’ll taste it in the final dish.

Storage

The soup keeps well for up to 3 days in the fridge in a covered container. Reheat it gently on the stovetop, then strain and portion into bowls just before serving. The beef is best cooked fresh to order as it dries out once cold and loses its crust on reheating. If you want to get ahead, slice the beef and have everything staged so assembly at serving time is fast.

FAQs

Can I make the soup ahead of time? Yes, and it actually improves with a night in the fridge. The flavours deepen and the soup thickens slightly as it rests. Make it up to 3 days ahead, cool completely, and store covered. Reheat gently on the stovetop, then strain into ovenproof bowls, top with Gruyère, and hit it with oven heat just before serving.

What cut of beef works best? I use ribeye off the bone for its fat marbling and flavour, but sirloin or rump both work well. The key is to slice it thinly, no more than a few millimetres, so it cooks through very quickly in the hot pan. Ask your butcher to slice it for you if you can, or partially freeze the beef for 30 minutes before slicing to make it easier to get thin, even cuts.

Can I use a different cheese? For the soup, Emmental or Comté are the closest substitutes to Gruyère and will both melt and flavour the dish well. For the sandwich filling, the Swiss cheese slices can be swapped for provolone or a mild Gouda. I’d avoid mozzarella as it lacks the savoury depth this dish needs, and cheddar tends to clash with the sweetness of the caramelised onions.