Roasted Celeriac and Hazelnut Soup with Crispy Sage and Sourdough

# Roasted Celeriac and Hazelnut Soup with Crispy Sage and Sourdough

Celeriac is one of those vegetables that tends to get overlooked in favour of its flashier cousins — but roast it properly and it transforms into something genuinely special. Nutty, creamy, and deeply savoury, this soup is the kind of thing you'll find yourself making on repeat through autumn and winter.

Why Celeriac Deserves More Attention

Celeriac (also called celery root) is the knobbly, unglamorous-looking root of a particular celery variety. Don't let appearances put you off — beneath that rough exterior is a dense, ivory flesh with a flavour somewhere between celery, parsley, and something almost earthy and nutty.

It's widely used across France, Germany, and Eastern Europe, yet it remains surprisingly underused in British home cooking despite being in season from late September right through to March. Most supermarkets stock it, it's usually very affordable, and it keeps well in the fridge for a week or more.

Roasting is the key step that makes this soup different from a standard blended celeriac recipe. The oven caramelises the natural sugars in the root, driving off moisture and concentrating that nutty depth — something boiling or steaming simply can't replicate.

The Full Recipe

Serves: 4 Prep time: 15 minutes Cook time: 50 minutes

Ingredients:

• 1 large celeriac (roughly 800g), peeled and cut into 3cm chunks
• 3 tbsp olive oil, divided
• 1 medium onion, roughly chopped
• 3 garlic cloves, unpeeled
• 750ml vegetable or chicken stock
• 150ml whole milk or oat milk
• 80g blanched hazelnuts, toasted
• 1 tsp white wine vinegar
• Salt and black pepper

For the crispy sage:

• 12–15 fresh sage leaves
• 1 tbsp butter or olive oil

To serve:

• 2–4 thick slices of sourdough, toasted or grilled
• A drizzle of hazelnut oil or extra olive oil
• A few reserved toasted hazelnuts, roughly chopped

Method:

1. Preheat your oven to 200°C (fan 180°C / gas 6). Toss the celeriac chunks with 2 tbsp olive oil and a generous pinch of salt. Spread onto a large baking tray in a single layer. Nestle in the unpeeled garlic cloves.

2. Roast for 35–40 minutes, turning once halfway through, until the celeriac is golden and caramelised at the edges. The garlic should be soft and sticky inside its skin.

3. While the celeriac roasts, heat the remaining tbsp of olive oil in a large saucepan over a medium heat. Add the onion and cook gently for 10–12 minutes until soft and lightly golden.

4. Toast the hazelnuts in a dry pan over a medium heat for 3–4 minutes, shaking regularly, until fragrant and lightly coloured. Set aside, reserving a small handful for garnishing.

5. Add the roasted celeriac to the pan with the onion. Squeeze the roasted garlic out of its skins and add that too. Pour in the stock and bring to a gentle simmer for 5 minutes.

6. Add the hazelnuts and milk, then blend until completely smooth using a stick blender or countertop blender. Add the white wine vinegar, taste, and adjust the seasoning.

7. For the crispy sage, heat the butter or oil in a small frying pan over a medium-high heat. Add the sage leaves and fry for 30–60 seconds until crisp. Remove quickly and drain on kitchen paper — they continue to cook after they leave the pan.

8. Serve the soup in warmed bowls with toasted sourdough, crispy sage, a few chopped hazelnuts, and a drizzle of oil.

What Makes This Work Nutritionally

This isn't just a pretty bowl of soup — it's actually a fairly well-balanced meal when served with the sourdough.

Celeriac is low in calories but genuinely high in fibre, vitamin C, vitamin K, and phosphorus. The fibre content is particularly useful here — it contributes to satiety and supports gut health without adding a heavy calorie load.

Hazelnuts bring the nutritional substance. They're a good source of monounsaturated fats (the same type found in olive oil), vitamin E, magnesium, and folate. They also add protein and fat, which slows digestion and helps this soup feel like an actual meal rather than a starter.

Sourdough is worth including deliberately rather than just as an accompaniment. The long fermentation process in real sourdough breaks down some of the phytic acid in wheat, which can improve the absorption of minerals like iron and zinc. It also tends to have a lower glycaemic impact than standard white bread.

The olive oil and hazelnut oil drizzled on top aren't just for aesthetics — fat helps the body absorb fat-soluble vitamins like vitamin K, which celeriac contains in meaningful amounts.

Per serving (approximate, including sourdough): 380–430 kcal, 12–14g protein, 18–20g fat, 42–46g carbohydrate, 7–9g fibre.

Common Mistakes That Flatten the Flavour

The biggest error people make with celeriac soup is not getting enough colour on the vegetable during roasting. Pale, steamed-looking celeriac makes a pale, flat soup. You want genuine caramelisation — golden-brown edges, some dark spots — before it comes off the tray.

The second mistake is skimping on seasoning. Celeriac needs salt. Not excessive amounts, but enough to bring out its naturally earthy-sweet character. Season the celeriac before roasting and then adjust again after blending.

Finally, don't skip the vinegar at the end. Just a teaspoon of white wine vinegar lifts the whole flavour profile by cutting through the richness of the hazelnuts and milk. It's the kind of adjustment you notice by its absence rather than its presence.

Variations Worth Trying

The base recipe is deliberately simple so it works as a canvas. A few directions worth exploring:

Make it vegan: Use oat milk and olive oil rather than whole milk and butter. The hazelnuts provide enough richness that you won't miss the dairy.

Add apple: A sharp eating apple (Granny Smith works well) roasted alongside the celeriac adds a subtle fruity acidity that plays nicely against the nuttiness. Peel, core, and cut into large chunks before roasting.

Swap the hazelnuts: Walnuts work well here and are usually cheaper. They bring a slightly more bitter edge which suits the earthiness of celeriac.

Make it heartier: Stir a dollop of crème fraîche through the finished soup and top with crispy bacon lardons or pancetta for a richer, more substantial version.

Storing and Reheating

This soup keeps well in the fridge for up to 4 days and freezes beautifully for up to 3 months. It will thicken as it cools — just add a splash of stock or water when reheating and stir to loosen.

Make the crispy sage fresh each time rather than storing it. Fried herbs lose their texture quickly and are worth the 60-second effort when you're ready to eat.

If you're meal prepping for the week, this is a strong candidate — it genuinely improves after a day in the fridge as the flavours deepen and settle.

Practical Takeaways

• Buy celeriac when you see it — it's in season from September to March and often the cheapest vegetable on the shelf during those months.
• Don't rush the roasting. Give the celeriac proper time and space on the tray. Crowded chunks steam rather than caramelise.
• Toast your hazelnuts fresh rather than buying pre-toasted — it takes four minutes and makes a noticeable difference to the depth of flavour.
• Finish with acid. White wine vinegar, lemon juice, or even a small splash of apple cider vinegar at the end transforms a flat soup into one that tastes properly finished.
• Batch cook. This recipe scales up easily. Double the quantities and you have lunches sorted for most of the week.

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