Celeriac is perfect for soup – even better when it's paired up with good-flavoured apples like russet or cox. You could also use sweeter cooking apples for this.
750g celeriac, peeled and roughly diced
1 bramley apple, peeled, cored and roughly diced
1.2ltrs vegetable stock
90ml double cream
2 x 1cm-thick slices of bread with the crusts removed
1tbsp olive oil
Salt and freshly ground black pepper
50g cheddar cheese, finely grated
Gently cook the celeriac in the butter, in a covered pan for about 5 minutes, giving the occasional stir and not allowing them to colour. Remove the lid, add the apple, cider and vegetable stock and bring to the boil. Season with salt and pepper and simmer gently for about 15 minutes until the celeriac is soft.
Blend in a liquidiser until smooth and strain through a fine-meshed sieve. Bring back to the boil, add the double cream and adjust with a little water or stock if it's too thick.
Meanwhile, cut the slices of bread into rough 1cm cubes. Heat the olive oil in a heavy-based or non-stick frying pan and fry the pieces of bread on a medium heat for a few minutes, turning them as they are cooking, until they are golden; transfer to a baking tray, scatter with the cheese and cook under the grill for a couple of minutes until the cheese has melted.
Serve in hot soup bowls and scatter the croutons on top.