Place chicken stock, pumpkin puree, onion, garlic, salt, thyme, and peppercorns in a large pot; bring to a boil. Reduce heat to low and simmer, uncovered, 30 minutes.

Transfer soup to a blender or food processor in batches; blend until smooth.

Return soup to the pan and bring to a boil; reduce heat to low and simmer, uncovered, for 30 minutes.

Stir in heavy cream. Ladle soup into bowls and garnish with fresh parsley.