Roll piecrust to 1/8" thickness on a lightly floured surface. Place crust in a 9" deep-dish pie plate; trim and flute edges, if desired. Cover and place in freezer while you prepare filling.
Cut butternut squash in half lengthwise. Place squash halves, cut sides up, in a shallow baking dish or pan. Bake, uncovered, at 350 degrees for 50 to 55 minutes or until squash is tender, basting often with butter. Cool slightly.
Remove and discard squash seeds. Remove squash pulp, discarding shells. Mash pulp. Place 2 cups mashed pulp in a large bowl. (Reserve any remaining mashed pulp for another use.)
Add 1 cup whipping cream and next 8 ingredients to mashed squash pulp; stir well with a wire whisk. Pour mixture into prepared pastry shell.
Bake at 350 degrees for 40 to 50 minutes or until set in center. (Shield piecrust with strips of aluminum foil to prevent excessive browning, if necessary). Cool completely.
Garnish each piece with a dollop of sweetened whipped cream; sprinkle each dollop with cinnamon.
Makes one 9" deep-dish pie.