1. Peel onions and thinly slice crosswise. Peel and core apples; thinly slice crosswise. Peel yams; cut in half lengthwise, then thinly slice crosswise.
2. Melt butter in a 5- to 6-quart pan over high heat. Crumble turkey into pan; stir often until no longer pink, about 4 minutes.
3. Add onions, apples, yams, sage, and caraway seed; cover and cook over medium heat, stirring occasionally, for 10 minutes. Uncover, turn heat to high, and stir often until liquid is evaporated and onions begin to brown, about 5 minutes.
4. In a small bowl, mix broth, sherry, and cornstarch. Add to turkey mixture and stir until it boils and thickens. Remove from heat and add salt and pepper to taste. Let cool to room temperature, stirring occasionally, 30 to 40 minutes. Spoon mixture into a shallow, round 1 1/2- to 2-quart casserole or a 10-inch pie pan that holds at least 6 cups.
5. On a lightly floured board, roll cream cheese pastry (or unfold and roll refrigerated pastry) into a round about 2 inches wider than the diameter of the casserole or pie pan. Center pastry over filling; trim edges to overhang rim about 1 inch. Fold overhang under pastry flush with rim. Flute pastry firmly against casserole or pan rim and slash top decoratively. If desired, reroll pastry scraps, cut into decorative shapes, and lay on top of pie.
6. Set pie on a foil-lined 12- by 15-inch baking sheet. Brush top with cream.
7. Bake in a 375° regular or convection oven until pastry is well browned and filling is bubbling, 35 to 45 minutes. If crust rim darkens excessively before center browns, fold foil from sheet up to cover rim loosely. Spoon pastry and filling from casserole to serve.