Heat the olive oil in a saucepan, add the onion and fry over a gentle heat until softened.
Add the garlic and cook for one minute.
Add the potato and celeriac and season, to taste, with salt and freshly ground black pepper.
Add the stock and cook for ten minutes, or until the potato and celeriac have softened. Remove the vegetables and stock from the heat and leave to cool for a few minutes, before blending with a stick blender. Alternatively do not blend fir a rustic style soup.
To serve, pour into a bowl and garnish with chopped chives.
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