Slow Cooker French Onion Soup

With the first spoonful, I knew I had to make it at home. This might not be the most authentic recipe and I apologise now to the French nation – I must confess to using Italian herb seasoning and Worcestershire sauce in my French onion soup.

Can you really make French onion soup in a slow cooker?

Absolutely. Making French onion soup in a slow cooker is not only possible, it’s the perfect method for achieving rich, caramelised flavour with minimal effort. Slow cooking allows the onions to soften and sweeten gradually, resulting in that classic deep, savoury taste. It’s ideal for busy days when you want comfort food ready with little fuss.

Do I need to caramelise the onions before adding to the slow cooker?

For extra depth of flavour, you can sauté the onions beforehand until golden brown – but it’s not essential. The slow cooker does a great job of softening and mellowing the onions over time. If you’re short on time, just toss everything in and let the slow cooker work its magic.

What cheese should I use for the topping?

Traditionally, French onion soup is topped with Gruyère cheese, which melts beautifully and adds a nutty richness. However, you can also use mature cheddar or mozzarella if preferred. Just be sure to grill the bread with the cheese on top until golden and bubbling.

Can I freeze slow cooker French onion soup?

Yes, French onion soup freezes very well. Let it cool completely, then portion into airtight containers and freeze for up to 3 months. Defrost thoroughly and reheat until piping hot. Just add the cheesy bread topping fresh when serving.

What can I serve with this slow cooker soup?

This soup is lovely as a starter or light meal, served with toasted baguette or cheesy croutons. For something more filling, pair it with a fresh salad or a warm sandwich. It’s a brilliant option for cold evenings or a stress-free dinner party starter.

Is this slow cooker French onion soup vegetarian?

Yes – if you use vegetable stock instead of beef stock, this recipe can easily be made vegetarian. For added richness, choose a good-quality stock and feel free to finish with a splash of balsamic vinegar for depth.

More slow cooker soup recipes

If you enjoy a slow cooker soup, you can check out more of my recipes:

• Slowcooker Vegetable Soup
• Slow Cooker Potato & Leek Soup
• Slow Cooker Carrot & Parsnip Soup
• Slow Cooker Tomato & Chilli Soup

And for more slow cooker recipes you can pick up my first ever cookbook The Healthy Slow Cooker Book or Slow Cooker Even Easier on Amazon today.