Cream of asparagus soup

Ingredients

• 50 gram butter
• 1 brown onion, chopped
• 1 leek, chopped
• 500 gram asparagus, trimmed, chopped
• 2 potatoes, peeled and chopped
• 1 litre (4 cups) chicken stock
• 1/2 cup (125ml) cream
• salt and pepper to taste
• 125 gram asparagus, finely chopped, extra
• chervil leaves, to garnish