In medium sized bowl, add the 2 1/2 cups of flour and salt. Mix with fork until combined.
Add in cubed butter and break up with a fork or hands. Mixture will still have lumps about the size of small peas.
Gradually add the ice water and continue to mix until the dough starts to come together. You may not need all of the water, but if the dough is too dry, then add more. The dough should not be very sticky.
Work the dough together with your hands and turn out onto a surface. Work into a ball and cover with cling wrap. Refrigerate.
Peel the apples, then core and slice.
In a bowl, add the sliced apple, cinnamon, nutmeg, and juice from the lemon.
Mix until combined and all the apples are coated. Refrigerate.
Preheat oven to 375°F.
On a floured surface, cut the pie dough in half and roll out both halves until around 3mm thick.
Roll out the dough around the rolling pin and unroll onto a pie dish making sure the dough reaches all edges. Trim the extra dough from the edges and pinch the edges to create a crimp. Make sure edges are sealed together.
Brush the pie with the beaten egg and lightly sprinkle with cinnamon sugar.
Cut four slits in the top of the pie to create a vent.
Bake the pie for 50-60 minutes or until the crust is golden brown and no grayish or undercooked pastry remains.
Allow to cool completely before slicing.
Top with ice cream and serve