Melt butter in large saucepan on medium heat. Add onion; cook and stir 5 to 7 minutes or until tender and lightly browned. Stir in squash, pears and broth. Cover. Bring to boil on high heat. Reduce heat to medium-low; cover and simmer 15 to 20 minutes or until squash is very tender. (Frozen squash will cook more quickly). Stir in 1 tablespoon of the coriander, sea salt and pepper.
With center part of cover removed to let steam escape, puree soup in batches in blender on high speed until smooth. Return pureed mixture to saucepan. Cook on low heat until heated through.
Mix yogurt and remaining 1 teaspoon coriander in small bowl until well blended. Ladle soup into bowls. Top each with a dollop of yogurt mixture.