Follow the steps in order for the best result.
In a large saucepan or stockpot, heat the oil over medium heat.
Add the chopped onion and diced celery. Cook, stirring occasionally, until softened but not browned, approximately 10 minutes.
Incorporate the Thai red curry paste, stirring continuously for about 1 minute until fragrant.
Incorporate the diced tomato, stirring continuously for about 2 minutes.
Introduce the pumpkin and mix until well coated with the curry paste mixture.
Pour in the vegetable or chicken stock.
Bring the soup to a boil, then reduce the heat to low, uncover, and simmer for 20 minutes, or until the pumpkin is very tender.
Take the saucepan off the heat and let the mixture cool slightly.
Using an immersion blender, food processor, or regular blender, carefully puree the soup until smooth. If using a standard blender, work in batches to prevent accidents.
Return the pureed soup to the saucepan and taste.
Season with salt, adding a teaspoon at a time and tasting after each addition, until the desired level of saltiness is achieved.
Stir in the coconut milk or cream, mix well, and taste again.
Adjust salt if needed.
Reheat the soup gently before serving.
For an elegant touch, garnish each bowl with a swirl of coconut cream or heavy cream and a sprig of fresh coriander.