To make roasted winter squash: Heat oven to 375°F. Heat butter over medium-high heat in an ovenproof sauté pan; add diced squash, salt and pepper. When squash begins to brown, place pan in oven. Roast for 15 minutes or until medium-brown on all sides. Remove from oven and let cool slightly. Puree in food processor, or mash with potato masher or ricer. Measure 1 1/2 cups squash; reserve.
To make soup: Heat the olive oil in a large saucepan over medium heat until hot. Add the onion, celery, carrot and cinnamon stick; sauté until soft but not brown, about 10 minutes. Season with salt and pepper. Add the broth and the coriander; bring to a boil. Simmer for several minutes. Stir in reserved squash until smooth; simmer gently to let the flavors meld, about 10 minutes. Discard the cinnamon stick.
Puree the soup using an immersion blender or in a blender until smooth. (The soup can be made ahead to this point, cooled, covered, and refrigerated for several days or frozen for about 1 month. It will thicken as it cools and may need thinning with broth or water when reheating.)
Return the soup to the pan and reheat gently. Add the half-and-half. Adjust the seasoning with salt and pepper. Top each serving with pumpkin seeds and toasted bread crumbs.