Place puff pastry sheet on floured surface. Cut into 9 (3-inch) squares. Place squares on ungreased cookie sheets. Bake at 400° for 10 minutes or until brown; cool on wire rack.
Combine pumpkin butter and next 4 ingredients; beat until light and fluffy.
Combine cream, vanilla extract, and 1/4 cup powdered sugar in a chilled mixing bowl. Beat until soft peaks form. Set aside 1/2 cup whipped cream and gently fold remaining whipped cream into pumpkin mixture. Cover and chill pumpkin filling at least 1 hour.
Carefully slice 1 pastry square in half to make 2 layers. Spoon about 3 tablespoons filling onto bottom layer; top with the second puff pastry layer. Repeat procedure with remaining pumpkin filling and remaining pastry squares. Chill up to 2 hours. Top each Napoleon with a dollop of reserved whipped cream. Garnish, if desired.
Pumpkin butter can be found in the jam and preserves section of your market. It is often seasonal. Substitute canned pumpkin if unavailable.