Heat the olive oil in a large saucepan over a medium heat and sweat the onions with some salt for 4-5 minutes until they start to soften. Sprinkle over the ground spices, stir and continue to cook for 1 minute. Add the pumpkin and continue to cook for 10 minutes, stirring occasionally. Add the stock to the saucepan, bring to the boil, then reduce the heat and simmer for 10-15 minutes until the pumpkin is soft. Stir in the Greek yogurt, then purée the soup with a stick blender until smooth; it should be quite thick. Season to taste, then spoon into serving bowls. Garnish with celery leaves (if available) and with a pumpkin on the side. Freezing and defrosting guidelines Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.