I spent an afternoon in a friend’s kitchen in Paris watching her make this soup. She sliced two pounds of yellow onions paper-thin, buried them in olive oil with thyme, garlic, and a bay leaf, and cooked them over the lowest possible heat for an hour. Not caramelised. Confit. Soft, sweet, translucent, and swimming in oil. Then chicken broth, heavy cream, thirty minutes of simmering, and a blender until smooth.
The cornstarch slurry at the end thickens it just enough to coat a spoon. Strained through a fine sieve, it becomes silky. Served with crusty bread and a spoonful of the confit onions on top. It tastes like someone spent an afternoon on it — because someone did.
Tips for Making Creamy Onion Soup
Confit the onions, do not caramelise them
Low heat, half a cup of olive oil or duck fat, one hour. The onions should be soft, sweet, and translucent, not brown. This is confit, not caramelisation. 
Stir occasionally. If the onions start to colour, reduce the heat further. The sweetness in this soup comes from slow cooking, not from browning sugars.
Blend and strain for a smooth texture
An immersion blender or regular blender until completely smooth. Then pour through a fine chinois or mesh sieve.
Straining removes any fibrous bits. The result should feel like velvet. If it is too thick, thin with a little more broth.
Creamy Red Onion Soup
- Total Time: 105 minutes
- Yield: Serves 4
- Diet: Omnivore
Description
Rich and decadent, this creamy onion soup is the ultimate comfort food. It pairs beautifully with a simple green salad or toasted bread topped with melted Gruyère.
Ingredients
- 2 lb (900 g) yellow onions, thinly sliced
- 1/2 cup (120 ml) olive oil or duck fat
- 4 sprigs thyme
- 2 cloves garlic, smashed
- 1 bay leaf
- Salt and black pepper, to taste
- 4 cups (946 ml) chicken broth
- 1 cup (240 ml) heavy cream
- 1 oz (28 g) cornstarch
- 2 tbsp (30 ml) cold water
- Salt and pepper, to taste
- Crusty bread or toasted baguette slices, for serving
- Chopped chives or caramelized onion slivers, for garnish
Instructions
- Prepare the confit onions: In a large heavy-bottomed pot, combine sliced onions, olive oil or duck fat, thyme, garlic, bay leaf, and a generous pinch of salt.
- Cook slowly over low heat, stirring occasionally, for about 45–60 minutes, until the onions are soft, sweet, and translucent but not browned. Remove the herbs and set the confit aside.
- In a separate saucepan, bring the chicken broth to a boil. Lower the heat and add the confit onions and heavy cream.
- Simmer gently for about 30 minutes to let the flavors meld.
- Blend the mixture with an immersion blender or in batches until smooth and velvety.
- Season with salt and black pepper to taste, then strain through a fine chinois or mesh sieve for an ultra-smooth texture.
- Return the soup to the pot and bring to a gentle simmer. In a small bowl, mix cornstarch with 2 tbsp cold water to make a slurry.
- Whisk the slurry into the hot soup and cook over low heat for about 10–15 minutes, stirring constantly, until slightly thickened.
- Serve hot with toasted baguette slices or crusty bread on the side.
- Garnish each bowl with chopped chives or a spoonful of caramelized onion confit.
Notes
- Confit onions are slowly cooked in fat until silky and sweet — they’re what give the soup its depth.
- Keep the heat low while cooking the onions to prevent browning.
- Duck fat adds richness, but olive oil works perfectly well.
- This soup pairs beautifully with a simple green salad or toasted bread topped with melted Gruyère.
- Leftovers can be blended again and used as a sauce for chicken or roasted vegetables.
- Prep Time: 15 minutes
- Cook Time: 90 minutes
- Category: Soup
- Method: Simmering
- Cuisine: French
Nutrition
- Serving Size: 1 cup
- Calories: 300
- Sugar: 5
- Sodium: 400
- Fat: 20
- Saturated Fat: 12
- Unsaturated Fat: 6
- Carbohydrates: 20
- Fiber: 2
- Protein: 5
- Cholesterol: 60
Frequently Asked Questions
Can I use duck fat instead of olive oil?
Yes. The recipe offers both. Duck fat gives a richer, more savoury flavour. Olive oil makes a lighter soup. Either works. Half a cup is the right amount.
What does the cornstarch do?
It thickens the soup slightly after blending. Mix one ounce of cornstarch with two tablespoons of cold water to make a slurry. Whisk it into the simmering soup and cook for ten to fifteen minutes.
Can I make this ahead?
Yes. The soup keeps in the fridge for up to four days and freezes well. Reheat gently over low heat. The cream may separate slightly when reheated, so whisk well.
Yummy this sounds so tasty and something new to try. Thanks for sharing.
Simon