Melt butter in a large pot over medium; cook onion and carrots 5-6 minutes until softened.
Add garlic; cook 1 minute until fragrant.
Add squash and apple; cook 3-4 minutes, stirring occasionally.
Add broth, sugar, cinnamon, nutmeg, and ginger; boil, reduce heat, and simmer 25-30 minutes until squash is very tender.
Off heat, puree with an immersion blender until completely smooth, or carefully transfer to a regular blender in batches.
Stir in cream; return to low heat and season with salt and white pepper.
Serve warm with toasted pepitas and a drizzle of cream if desired.