Preheat oven to 325 Deg F. Combine mashed sweet potatoes, sugars, egg, cream, vanilla, salt, cinnamon, allspice, nutmeg and butter in an electric mixing bowl and beat at medium-low speed until smooth, do not overmix.
To assemble pie, spoon sweet potato filling into the pastry-lined pie pan. Fill shell evenly to the top with with pecan filling. Bake 1 1/2 hours or until a knife inserted into the center of the pie comes out clean. Store pie at room temperature for 24 hours. Serve pie slices with Bourbon Sauce on top or to the side.
Prepare Pecan Pie Filling: Combine sugar, syrup, eggs, butter, vanilla, salt and cinnamon in an electric mixing bowl and beat on low speed until syrup is opaque, about 4-5 minutes. Stir in pecans, mix well.
Prepare Bourbon Sauce: Combine cream and milk in a large mixing bowl. Slowly whip in pudding mix. Add bourbon and continue whipping. Add vanilla and whip until mixture is well blended to sauce consistency (should not be as firm as pudding, but should not be runny). Sauce should be made about one hour before use; it will thicken as it sits.