In a large saucepan over medium heat saute onions in the butter and oil until translucent; add the pumpkin or turnip and saute for 2 to 3 minutes. Add the stock, lemon zest and nutmeg and bring to a boil. Reduce heat and simmer about 20 minutes, covered, until pumpkin or turnips are cooked. Remove from heat. If the stock is too thick, thin with additional stock. In a food processor or blender puree the mixture in small batches and return mixture to pot. Add salt and pepper; heat and serve in preheated bowls or hollowed out pumpkin, if using. Top each serving with sour cream and chives or parsley.
