To make the pastry crust: Sift the flour and salt into a large bowl. Cut the butter and Crisco shortening into the flour by pulsing in a food processor (or do it by hand using a pastry blender) until the texture resembles coarse meal with bits of butter.
Stir the egg into the flour mixture and pulse until incorporated. If the dough does not hold together, add ice water, half a tablespoon at a time, pulsing after each addition.
On a lightly floured work surface, pat the dough pastry into a disc. Cover in plastic wrap and refrigerate at least 1 hour or up to 2 days. Or wrap dough well in plastic wrap (twice) and freeze the dough for later use.
To make the filling: In a large skillet, saute onions till transparent. Add cubed potatoes, carrots and cook till soft, about 8 minutes.
Add the cooked chicken or turkey to the potatoes. Pour the broth or soup stock. Cook the potatoes, carrots and chicken (or turkey) together for 5 minutes more. Add the sour cream. Cook till liquid reduces for about 6 minutes and the meat has absorbed most of the broth. Season with salt and pepper. Remove from stove and set aside to cool before filling into pastry.
To assemble empanadas: on a dry, floured surface, roll out the pastry dough to about 1/8 inch thickness.
With a sharp knife, slice the dough into a rectangle, measuring about 6 inches x 4 inches in diameter.
Fill half the dough piece with a tablespoon of chicken (or turkey) and potato filling.
Brush egg wash on the inside edges. Fold dough in half and seal with a fork.
Place empanadas on a baking sheet lined with parchment paper. Brush empanadas with egg wash consisting of one beaten egg and 2 tablespoons of milk.
In a preheated oven of 375 degrees, bake empanadas for 20-23 minutes. When done, cool on counter.
Cook's comments: you can bake these empanadas ahead of time and freeze them in sealed plastic containers. I make these ahead, wrap them in individual resealable sandwich bags and freeze them. My family takes them out one at a time, for lunchboxes or "merienda" (snacks).