In a large sauté pan or skillet over medium-high heat, brown the pork. (You may need to do this in two batches, depending on the size of your pan). Add onion, garlic, white wine, sage, allspice, cloves, nutmeg and cinnamon. Simmer, uncovered, for 20 minutes, stirring occasionally.
Stir in turkey, thyme and garlic powder; continue cooking for another 15 minutes or until the wine has evaporated. Remove from heat and stir in mashed potatoes. Season to taste with salt and pepper. Adjust other seasonings as needed. Set aside.
Roll one of the pie crusts to around 12 inches. Place in a 9-inch, deep dish pie plate and gently press into bottom and sides. Brush the bottom crust with the mustard. Spoon in meat mixture, pressing down and smoothing the top as needed to get rid of any air pockets.
Roll second crust to 9 inches and place on top. Fold or roll in excess dough around the rim, pressing and/or pinching to seal. This will make a nice rim around the top. You can mold the edge into a fluted rim if you like. Cut four 3- to 4-inch slits in the top of the crust to release steam.
Bake for 45 minutes or until hot and the top is nicely browned. Serve immediately.
Make ahead: The tourtière can be assembled but not baked, wrapped tightly in foil and frozen for up to one month. Thaw before baking. It can also be prepared and cooked up to 24 hours in advance, covered and refrigerated. Reheat in a 375 degree oven for 30 to 40 minutes.