In a large pot or soup pan, heat 2 ½ tablespoons oil over medium heat. Once hot, add 180 g red onion, 5 cloves garlic, and 2 stalks celery. Cook gently, stirring occasionally, until softened.
Add 2 sweet potatoes and 500 g pumpkin to the pot.
Add 1 handful fresh coriander, ½ teaspoon turmeric powder, ½ teaspoon red chilli powder, 1 teaspoon cumin powder, and ⅛ teaspoon cinnamon powder. Stir to coat the vegetables in the spices, and let this mixture cook for around 30 seconds, stirring occasionally to stop the spices catching on the bottom of the pan.
Add 1 litre vegetable stock to the pot and simmer on medium heat until the sweet potato and pumpkin have fully softened and cooked through — around 30 minutes.
Switch off your stove and use an immersion blender* to puree the soup until thick, smooth, and creamy. Beware! The soup is hot and can splash, so exercise caution.
Add 150 ml double cream, freshly ground salt and pepper, and optionally, lemon or lime juice. Taste and adjust the seasonings to your preference, then serve.
Notes
* Alternatively, you can allow the soup to cool and use a countertop blender.