In a food processor, combine the flour and salt. Pulse to combine. Add the butter and shortening and blend well. Add the egg yolk and then with the food processor running, slowly add the milk until the pastry comes together. Wrap the pastry in plastic wrap and chill for at least an hour or overnight.

Divide the pastry and roll it out, a bit thinner than a pie crust. Cut into circles using a 5 or 6 inch bowl as a stencil. Chill the discs until ready to use, separated with wax paper or plastic.

Spoon a filling into the center of each disc and seal, crimping according to Marcello Marini's directions (pinch and turn 13 times - https://www.click2houston.com/houston-life/2018/10/02/recipe-beef-empanadas/ at about 2:30). Filled empanadas should be chilled until frying and can be frozen at this point. Fry at 375 for 3 minutes or until browned. Alternately bake at 400 for 10 minutes.

It shouldn't need to be said, but the filling needs to be cold. Hot filling will result in pastry that just falls apart (this comment would not be here if this had not been done at least once).