"creamed potato and pumpkin soup"

Ingredients

• - 2 ounces butter or 2 ounces margarine
• - 2 onions , peeled and sliced
• - 1 garlic clove , crushed
• - 2 lbs pumpkin , peeled and diced
• - 12 ounces potatoes , peeled and diced
• - 1 ½ teaspoons tomato paste
• - 2 ½ cups chicken stock or 2 ½ cups vegetable stock
• - salt & freshly ground black pepper
• - 1 teaspoon lemon juice
• - ½ teaspoon ground allspice
• - 2 ½ cups milk
• - 6 tablespoons sour cream
• - freshly chopped coriander (cilantro) or parsley (to garnish)