Melt butter in a large saucepan.
Saute onion until tender.
Add carrots and tomato paste.
Cook for 1 minute.
Blend in water and stock cube.
Bring to the boil.
Simmer, uncovered, for 30 minutes.
Stir in mushrooms, sherry, spices and seasonings.
Simmer for a further 10 minutes.
Sprinkle with chives.