Let rolled pastry stand at room temperature according to package directions. Meanwhile, in a large saucepan cook sweet potatoes in enough lightly salted boiling water to cover for 15 minutes or until tender. Drain; return to saucepan. Use a potato masher to mash potatoes until smooth. Measure 1 1/2 cups potatoes.
Place one pastry on a lightly floured surface. Roll to a 14-inch circle. Brush with 1 Tbsp. melted butter. In a small bowl combine granulated sugar and 1 tsp. cinnamon. Sprinkle cinnamon-sugar mixture over pastry; press lightly with fingers. Roll pastry into a log. Pinch to seal edge and ends. Cover; chill until needed.
Preheat oven to 450 degrees F. Unroll remaining pastry into a 9-inch pie plate. Fold under extra pastry even with edge of plate. Crimp edge as desired. Do not prick pastry. Line pastry with a double thickness of foil. Bake 8 minutes. Remove foil. Bake 4 to 5 minutes more or until set and dry. Remove from oven. Reduce oven temperature to 350 degrees F.
In a large bowl whisk together eggs, milk, sour cream, bourbon, and vanilla. Stir in the 1 1/2 cups sweet potatoes and remaining 2 Tbsp. melted butter. Stir in brown sugar, flour, remaining 1/2 tsp. cinnamon, the salt, and nutmeg until combined.
Pour sweet potato mixture into piecrust. Cover edge with foil to prevent overbrowning. Bake 30 minutes. Cut chilled log into 1/4-inch slices. Remove pie from oven. Remove foil. Carefully arrange pastry slices on top of filling, placing them close together but not overlapping. Bake 25 minutes more or until filling is puffed and set and cinnamon-sugar spirals are light brown. Cool on a wire rack. Cover; chill within 2 hours.