Heat the oil in the pot on medium heat. When the oil is shimmery, add in the onions. Sauté for about 5 minutes, until the onions are soft and just starting to brown.
In the meantime, as the onions cook, peel the carrots and sweet potato. Cut the carrots into 1-inch pieces. Cut the sweet potato into about 1-inch pieces. No need to be precise.
When the onions are ready, add in the carrots, sweet potatoes, minced ginger, pumpkin pie spice and white pepper. Cook for another 2 minutes, stirring regularly.
Add in the chicken broth, water and thyme. Bring to a simmer, then turn down the heat. Simmer for 30 minutes, covered, stirring occasionally, until the carrots and sweet potato are tender.
Remove the stalks of thyme. Blitz with a stick blender until smooth. When blitzing, make sure the hot soup does not splash out. Alternatively, you can allow the soup to cool slightly, then transfer it to a blender and blitz until smooth. Lastly, stir in the coconut milk. Serve and enjoy.