Bring first 3 ingredients to a boil in a large saucepan; reduce heat, and simmer until reduced by half. Remove and discard bay leaf. Stir in mashed pumpkin.
Process white wine mixture in a blender until smooth, stopping to scrape down sides. Return mixture to saucepan, and whisk in whipping cream. Cook sauce over medium heat, whisking occasionally, 5 minutes.
Whisk in butter and remaining ingredients.