Peel and chop the onion. Peel and wash the potato and cut into small cubes. Heat the fat in a saucepan and fry the onion and potato. Add 3/4 l water and stock. Bring to the boil, cover and simmer for about 10 minutes.
Add 3/4 of the frozen peas, bring to the boil again and continue cooking for about 5 minutes. Wash the coriander, shake dry and pluck off the leaves. Add to the soup except for a little garnish. Add cream.
Puree the soup very finely with a hand blender.
Add the remaining peas to the soup and bring to the boil again. Season with salt, pepper, 1 pinch of sugar and lemon juice. Sprinkle with remaining coriander.