Preheat oven to 425F.
Put diced potatoes in a saucepan. Cover them with water, add salt, and bring to a boil. Simmer until soft. Drain, and set aside.
Melt butter in the saucepan. Add onion. Cook until onion is soft and translucent, about 3 minutes.
Add salt & pepper.
Sprinkle flour into the saucepan. Mix well with the butter mixture until light brown, about 1 minute.
Whisk in chicken stock and milk. Add thawed vegetables and potatoes. Let mixture simmer until thickened, stirring occasionally.
Stir in ham.
Prepare first pie crust as per its normal directions in a deep dish 9" pie pan.
Spoon in filling.
Place second pie crust on top, and trim the excess around the perimeter of the pie. Press the two crusts together, and use your fingers to crimp the edges.
Brush the top of the pie with the egg wash. Cut 4-6 slits in the top crust to allow steam to escape.
Place on a baking sheet. Bake for 30 minutes. Serve and enjoy warm!