Stir in sugar, milk and egg. Dough should be soft but not sticky. Try not to over mix. Add a little more flour if too sticky.
Turn dough out onto a floured board. Cut the dough into two portions.
Place half of the dough into the prepared tart pan, pressing it in with floured fingers to evenly cover the bottom of the dish.
Spread the apple slices evenly over the base, leaving a bit of an edge all the way around. Sprinkle with the brown sugar and cinnamon, evenly.
Carefully roll out the remaining half of the dough into a circle roughly the same size as the dish. Place on top of the apples, pressing the edges together with the bottom crust. ( the crust is very pliable, if need be, place on top of apples and spread with fingers to cover apples, and pinch together with bottom crust).
Cut several slits in the top of the cake to ventilate.
Brush the top with egg, and sprinkle with 1 - 2 tablespoons of sugar. Bake for 30 - 35 minutes or until golden brown, and apples are tender. I use a narrow knife to check apples..if easily goes through them it's done. Mine took 30 minutes.