Combine sugar, butter, and salt in a food processor or with an electric mixer, beating at high speed just until mixture is creamy (about 30 seconds).
Add the egg, vanilla, and milk and beat until blended.
Add 1 1/3 cups flour and beat just until blended (do NOT overmix).
With floured hands, shape the dough into a round, flat patty.
Lightly dust with flour, cover, and let sit for at least 1 hour before rolling out (will keep for several days).
In a large skillet, melt the margarine over high heat; saute the onions and celery until wilted, stirring occasionally (about 4 minutes).
Reduce heat to medium and add the pork, garlic, and seasonings.
Cook for 4 minutes, stirring often; breaking up any large chunks and scraping the bottom of the pan (lower the heat if the onions start to turn dark brown).
Add the beef and mix thoroughly.
Lower the heat and let simmer for 5 minutes, stirring often.
Mix in the potatoes and the stock.
Cook for 10 minutes over med-low heat, stirring often.
Strain the mixture very well and let cool at least 15 minutes before filling the pie shell.
On a lightly floured surface with a floured rolling pin, roll out the dough to fit a 1.5" deep/8" round cake pan (dough should be 1/4" thick) or divide dough into 4 equal parts and then roll each out to 1/8" thickness.
If making one large pie, grease and flour the cake pan and fit the dough inside, firmly pressing the bottom and the sides; trim the edges even with the top of the pan.
Refrigerate dough for 15 minutes.
Arrange pie weights or dried beans evenly on top of the dough, and bake at 350F for 20 minutes.
Remove weights and bake just until the crust on the bottom part looks dry (15 minutes).
Let cool for 5 minutes.
In a small bowl, mix the ingredients listed under topping until smooth and thoroughly blended.
Spoon the meat filling into the pie crust and spread the cheese topping evenly over the filling, being careful not to mix the two.
Bake at 350F until the crust is golden brown (40-45 minutes).
Let cool 10 minutes before serving.
If making individual pies, place a plate upside down on each section of dough and trim around the edge to make it perfectly round.
Place 1/4 of the filling to one side of the circle and spread the filling evenly over that half to within 1/2" of the edge.
Fold the circle in half over the filling and seal by pressing the edge with a fork.
Trim the edge to 1/4".
In a deep pan or deep fryer, heat at least 2 inches of oil to 350°F.
Hold the pies under the surface and cook until a rich golden-brown (1 1/2-2 minutes), then drain on a paper towel.