The recipe puts yellow onions, butter, garlic, and thyme into the slow cooker on HIGH. They caramelise for up to seven hours into a dark, sweet mass without any stirring. Beef stock and white wine go in for the last 30 minutes, and the whole thing serves 5.

The slow cooker handles what a hob cannot for this recipe. Onions on the hob brown at the edges but stay sharp in the centre unless you watch them for an hour. Sustained, even heat converts them fully, which is what gives the broth its deep, savoury base.

The bread goes under the grill before it goes into the soup. Untoasted bread in hot broth collapses within seconds into a soggy mass that sinks to the bottom. Grill the slices first, then build each bowl, and you get the crisp crust and bubbling Gruyère.

Slow Cooker French Onion Soup

Recipe by Shili MohamedCourse: SoupsCuisine: FrenchDifficulty: Easy

Servings

5

servings

Prep time

25

minutes

Cooking time

6

hours 

Calories

593

kcal

Caramelised yellow onions sit in the slow cooker on HIGH for up to seven hours before beef stock and white wine go in. The soup finishes under the grill with toasted bread and Gruyère melted in each oven-safe bowl.

Ingredients

• Soup

• 28g unsalted butter

• 1.3kg yellow onions, thinly sliced into half-moons

• 4 garlic cloves, minced

• 1 tsp fresh thyme leaves (or ½ tsp dried thyme)

• Salt and black pepper, to taste

• 1 litre beef stock

• 120ml dry white wine

• To Finish

• 1 French baguette, cut into slices

• 50g Gruyère, grated

Directions

• Add the butter, sliced onions, garlic, thyme, and a generous pinch each of salt and pepper to a 6-litre slow cooker. Stir to combine.
• Cook on HIGH for 5 to 7 hours, until the onions are deeply caramelised and a dark golden colour. Stir once or twice if you are around.
• Pour in the beef stock and white wine. Cook on HIGH for a further 30 minutes.
• About 10 minutes before serving, place the baguette slices on a baking tray and grill until toasted, about 2 to 3 minutes.
• Ladle the soup into oven-safe bowls. Place one or two toasted baguette slices on top of each portion and scatter the grated Gruyère over the bread.
• Place the bowls under the grill for 1 to 2 minutes until the cheese is melted and beginning to bubble. Serve immediately.

FAQs

How should I slice the onions for this recipe?

Thin half-moons, about 5mm thick, give the onions enough surface area to caramelise evenly. Thicker slices survive the long cook with more texture, but the caramelisation is uneven and the broth picks up less sweetness. A mandoline speeds the prep if you have one; a sharp knife works equally well.

What can I use instead of Gruyère?

Emmental is the closest substitute: same melt, similar nuttiness, slightly milder flavour. Comté works equally well and has more depth, though it is pricier and harder to find in most supermarkets. Swiss cheese melts cleanly and keeps the bowl looking right, though the flavour is less complex than either.

Can I leave out the white wine?

Leaving it out is fine: swap it for the same amount of additional beef stock. The wine adds acidity that brightens the broth after hours of caramelisation, so without it the soup runs slightly flatter. A tablespoon of wine vinegar stirred in at the end restores some of that sharpness.

What if I want another slow cooker soup this week?

A tomato and beef base covers entirely different ground from the caramelised onion broth here. A slow cooker lasagna soup on easypeasyslowcook.com uses the same pot and gives the week genuine variety. The pasta and cheese base make it a complete meal without needing anything else alongside.

What slow cooker main goes well after this as a starter?

Bolognese works well because the register shifts from a light, savoury broth to something richer and more filling. A slow cooker Bolognese on easypeasyslowcook.com runs on beef and tomato and needs no attention while this soup is still going. Two slow cooker recipes across one day with no overlap in effort.