Heat olive oil in a soup pot or Dutch oven over medium-high heat. Add the onion and cook, stirring occasionally, until soft, about 5 minutes. Add the garlic, ginger, and curry powder, and cook, stirring, for another minute. Add the broth, pumpkin, ½ teaspoon salt, and ½ teaspoon pepper. Bring to a boil, reduce heat and simmer, uncovered, for 15 minutes, stirring occasionally.
Take off the heat and stir in the coconut milk. Let cool. Puree the mixture in a blender until smooth. Refrigerate until cold, at least 4 hours. Taste and add more salt and pepper, if desired.
Prior to serving, combine the heavy cream and sour cream in a mixer fitted with the whisk attachment. Beat on medium-high speed until soft peaks form.
To serve, pour about 4 ounces of soup into a small glass or mason jar and top with a dollop of the whipped cream