Sift flour and salt together into a medium bowl. Cut in the butter and shortening with a pastry blender or two knives used scissor fashion until mixture resembles coarse crumbs. Stir in 4–5 tablespoons of ice water until dough just holds together.

Divide into 2 even balls and pat each into a disk, wrap in plastic wrap and refrigerate while you make the filling.

Melt the butter in a medium saucepan over medium-low heat; add the apples, lemon, flour, brown sugar, cinnamon, nutmeg and salt. Cook 20 minutes stirring often. Remove from heat and stir in vanilla. Allow to cool.

Line 2 large baking sheets with parchment paper. Beat the egg with 1 tablespoon water.

On a floured surface roll the pie crusts out (one at a time) to a 10 x 13 inch rectangle. Use a pastry or pizza cutter to cut 9 (3 x 4 inch) rectangles out of each. Then reroll the scraps to make 2 additional 3 x 4 inch rectangles.

Place 6 of the crusts on the baking sheet 1 or 2 inches apart. Place a rounded tablespoon of apple filling in the center and gently spread out leaving about a ½ inch border around the edges. Brush egg white around the edges and top with another piece of crust. Crimp the edges all around with a fork. Brush with egg white all over. Repeat until you have 10 pop-tarts.

Refrigerate the pop-tarts on the baking sheets for 20 minutes. Preheat oven to 375 degrees F.

Bake one sheet at a time 15-16 minutes until golden brown all over. Remove to wire racks to cool.

To make the glaze add the brown sugar, butter and milk to a small saucepan over medium heat and bring to a boil, stirring often. Remove from heat and allow to cool to lukewarm. Brush over tops of the pop-tarts and decorate with sprinkles.