1.Cut the pumpkin in half crossways with a large sharp knife. Scoop out the seeds with a spoon, then peel the pumpkin with a vegetable peeler or sharp knife. Chop the pumpkin coarsely.
2.Peel the kumara and potatoes with a vegetable peeler. Rinse well under cold water. Chop coarsely.
3.Peel then coarsely chop the onion. Peel then crush the garlic.
4.Melt the butter in a large saucepan on the stove over medium heat. Add onion and garlic to the pan; stir with a wooden spoon about 5 minutes or until the onion is soft.
5.Stir the stock into the pan. Put the lid on the saucepan. Turn the stove on to high and heat until the mixture boils. Carefully add the pumpkin, kumara and potato to the pan. Put the lid back on and heat until the mixture boils. Reduce the heat to medium-low. Simmer for about 15 minutes or until the vegetables are soft when tested with a fork or skewer. Remove the soup from the heat; stand for 10 minutes with the lid off to cool slightly.
6.Blend the soup in the pan with a stick blender until smooth. (Or, ladle about one-third of the vegetables and liquid into a blender or food processor. Blend or process until the soup is smooth. Pour the soup into a large jug or bowl. Repeat with the remaining soup mixture, then return the soup to the pan.)
7.Add half the cream to the soup. Season to taste with salt and pepper. Turn the stove on to medium heat; stir the soup until heated through.
8.Using a ladle, divide the soup into six serving bowls. Spoon one tablespoon of the remaining cream on top of each bowl; sprinkle with the chives.