Preheat the oven to 375F with a rack positioned in the center of the oven.
Empty the jar of mincemeat into a medium bowl. Peel, core and chop the apple. Mix into the mincemeat mixture. Add the grated zest of one lemon. Set aside.
Mix the flour and the butter until the mixture resembles breadcrumbs. Add in the sugar and mix well. Then add the beaten egg and three tablespoons of milk. The mixture should come together to a dough. Add a little more milk if needed.
Roll out the dough to one 1/8-inch thickness and cut out the dough to large enough circles to fill the bottom a mini quiche pan. For my pan, circles that are two inches in diameter work well. Press the dough down with mini tart tamper tool.
Place one tablespoon of the filling in the pies.
Put a little water into a small bowl. One tablespoon of water should work fine. Dip your finger into the water and run your finger along the edge of each pie.
Make cut outs to cover the pies. I started with circles that are two inches in diameter. Lay each circle flat on top of each pie.
Press to seal. I used a champagne flute to press and seal. Invert the champagne flute and press down of the dough. Twist to release the excess dough. Peel away the excess dough. Note: The champagne flute I used is slightly has a diameter of slightly under 2 inches. It creates the domed look that you see in the pictures.
Brush with egg wash.
Bake in the oven for 15 minutes or until the edges turn a light golden brown.
Remove from oven to a wire rack and allow the pies to cool.
Run a blunt knife if needed, around the edge to release. The pies should come out easily.
Sprinkle with confectioner's sugar if desired.