First, dice and roast the celeriac.
Peel the onion and garlic, and roughly chop.
2 onions, 2 cloves garlic
Put the olive oil into a medium sized saucepan, and fry the onion over a medium heat for a few minutes, stirring all the time. Then add the garlic and cook for another couple of minutes until the onion is translucent, turning golden at the edges and is fragrant.
2 tbsp olive oil
Core the apple and cut into chunks (no need to peel).
1 apple
Add the roasted celeriac, apple, parsley and stock to the pan, give it a good stir and add some pepper and salt. Put the lid on and bring to a simmer. Then turn the heat right down and leave to simmer gently for 20 minutes.
1 litre vegetable or chicken stock, 20 g parsley, 1 celeriac
Once the vegetables are all very soft, whizz the soup with an immersion or stick blender. (If you prefer, you can use a blender or food processor.)
Taste and adjust the seasoning or add a little more stock if the soup needs thinning.
Stir in the lemon juice. If you like a creamier soup, you can also add a knob of butter.
½ lemon
Serve garnished with fresh herbs and a drizzle of cream.