French onion soup is a classic. Like Roasted Tomato Basil Soup, Thai Red Curry Chicken Soup or Ukrainian Borscht, these classic soups remain our favourites year after year. A simple, yet elegant, classic soup comfort dish doesn't usually need to be messed around with. Unless, of course, you're making it with beer! This recipe for French Onion Soup with Lager is one of our favourite ways to tweak the classic just a little, in a delicious way.

French onion soup in a white bowl with a spoon.

What Makes French Onion Soup So Good With Lager?

The sweetness of caramelized onions, beefy broth and melted cheese is a perfect marriage with the crisp, smooth, and slightly malty flavour that a lager adds to the recipe. You won't taste the beer in the end product, but you will notice a depth of flavour and brightness to an otherwise earthy, sweet bowl of soup.

Two bowls of soup on a wooden cutting board.

Ingredients For This Recipe

This may be an elegant French recipe, but it has surprisingly few ingredients. However, those few ingredients need to be the best you can find.

Onions

My first choice for French onion soup are sweet onions, such as Vidalia, Walla Walla, or Maui onions. However, you can always use yellow onions, which are the most common variety, and one that you more than likely have in your kitchen. Yellow onions still have lots of sugars, so they will cook down beautifully, as well.

Because they are the star of this show, you want the freshest onions possible. When shopping, look for firm, unblemished onions, and pass over any that have sprouted.

Butter

This is a French dish, and butter is a given. Butter adds richness and helps the caramelization process along. However, you can use olive oil if you prefer, and your soup will still be delicious.

Beef Stock

Homemade stock is nice, but if you don't have it, use a good quality, low sodium stock found in a carton. You can use chicken stock for a lighter version of French onion soup, but it will lack the rich flavour that beef stock imparts. You can also use vegetable stock for a delicious vegetarian version.

Beer

A pale lager is ideal for this French onion soup with beer recipe. Lager, as opposed to Ale or Stout, is a lighter beer, which will not overpower the sweetness of the onions, but rather enhance and elevate it. A lager's nice, low-intensity balance of hops and malt is ideal for the beer that you choose.

Keep in mind, when you use beer in your cooking, use the same rule of thumb as you would when cooking with wine. If you wouldn't want to drink it, don't cook with it.

Seasonings

This soup is seasoned very simply; just a bay leaf, fresh thyme, Worcestershire sauce, and salt and pepper. Don't skip the bay leaf if you can help it. It may seem as though it doesn't add much, but it really does! If you don't have fresh thyme, substitute 1 teaspoon of dried thyme leaves. Use a gluten-free Worcestershire sauce if needed.

Bread

A slice of crusty French bread or artisan sourdough are perfect toppings for your soup. You can even use leftover garlic bread. And it's totally OK if your bread is a little stale. It's going to be toasted and eventually soak up all of that beefy, sweet caramelized onion goodness. And then be covered in toasty melted cheese. However, my favourite bread for this French onion soup with lager recipe is a baguette. Being smaller in diameter, a baguette has more crusty surface. I use 2 or three slices for each serving. Use a gluten-free baguette or French loaf if you prefer.

Cheese

Gruyere is the traditional cheese for topping French onion soup. While gruyere is definitely the preference, Swiss cheese is a close second. Mozzarella will work in a pinch, but you will be missing out on the depth of flavour that gruyere brings to the dish. If you do use mozzarella, I suggest using a blend of mozzarella and freshly grated Parmesan cheese in a 60/40 ratio.

Always grate your own cheese rather than use pre-grated, which can be of questionable freshness and may contain preservatives and anti-caking agents.

A baguette and a bowl of shredded cheese to be used in the soup recipe.

Pro Tips For the Best French Onion Soup

Slice the onions thinly. You can use a sharp knife, a mandolin, or use a food processor to make short work of it, if you have one. If you are using a food processor to slice the onions, use it first to grate your cheese since you already have it out and set up anyway.
It's going to seem like you have a LOT of onions. But don't worry, the caramelization step reduces the onions to the perfect amount for the recipe.
Caramelize the onions: this is the key to perfecting this classic recipe. Although it takes time and patience to properly caramelize onions, it isn't hard and it's more than worth the time spent. See below for onion caramelizing tips.
Scrape the pan to deglaze it when adding the liquid to take full advantage of all the flavourful brown bits leftover from carmelizing the onions.
Toast the bread: it's very important that the bread topping is toasted. Toasting allows the bread to resist soaking up the hot broth entirely, allowing for some nice crusty crunch.
On that note, be sure to serve the soup immediately after it comes out from the broiler, in order to avoid soggy bread toppings.
Set bowls on a baking sheet before you put them under the broiler. This makes the bowls easier to transfer in and out of the oven and catches any messy spills.

How To Caramelize Onions

French onion soup is a classic but very simple dish. It's super easy to make. But it's essential to keep in mind, that the key to the best onion soup is the slow caramelizing of your onions. You want to cook them slowly on low heat until they turn a golden brown. This is the most important part of the recipe. When you slowly caramelize the onions, it brings out their sweetness and adds an important depth of flavour to your soup. However, be sure to stop cooking when your onions are golden brown. If you keep going, and the onions become too dark, they can become bitter. And we are looking for sweetness, not bitterness.

Variations

Make it Vegetarian

This can be a vegetarian soup by substituting vegetable stock for beef stock.

Make it Gluten-Free

Use gluten-free beer, gluten-free Worcestershire sauce, and gluten-free French bread or baguette to make the recipe gluten-free.

Make it Ahead

Make the soup up to step 4. Allow to cool, then refrigerate in an airtight container for up to two days. When you're ready to complete the recipe, reheat the soup to a simmer, then continue from step 5.