Leave the seeds in the chipotle if you like your soup very spicy.
Melt butter in a Dutch oven over high heat. Add onion; sauté until lightly browned, 3 to 4 minutes. Reduce heat to medium-high; cook, stirring occasionally, until onion is soft and translucent, about 4 minutes. Stir in oregano and garlic; sauté for
minutes. 2 Whisk together flour and ¼ cup of the broth. Add flour mixture, sweet potatoes, chipotle, adobo, orange zest, salt, cinnamon and remaining 5¾ cups broth to onion mixture. Bring to a boil over high heat. Reduce heat to medium; cover and simmer, stirring occasionally, until sweet potatoes are very tender, about 15 minutes. Remove from heat; let cool for 10 minutes.
Transfer mixture, in batches, to a blender. Remove center piece of blender lid to allow steam to escape; secure lid. Place a clean towel over lid opening to avoid splatters. Blend until smooth. Return to pot.
Whisk together crème fraîche and water. Add additional water, if necessary, until mixture is thin enough to drizzle. Ladle soup into bowls; drizzle soup with crème fraîche mixture and sprinkle with pumpkin seeds.