Chicken Pot Pie

This pie is the definition of "comfort food". A cold day, nice glass of chardonnay, a fire in the fireplace...just warms the heart, doesn't it?
Let me say that a pot pie must have a top and bottom crust.
Crust -
2 1/2 C all purpose flour
1/2 t salt
1 stick butter (cold, cut into pieces)
4 T shortening
2 eggs (seperated)
4 T cold water
Filling -
1/4 C butter
1/4 C extra virgin olive oil
1 small onion (chopped)
2 stalks celery (diced)
1 lg carrot (diced)
3 lg cloves garlic (smashed, minced)
1/4 lb mushrooms (sliced)
1 C fresh or frozen peas
Salt & pepper to taste
4 C cooked chicken breast (boil chicken breast with breast bone and w/out skin in water about 20 mins until done. Remove bones and cube)
4 C chicken stock
4 T all purpose flour
Crust -
Sift flour & salt into a bowl. Cut butter and shortening into flour w/ pastry cutter until mixture is crumbly. Beat the yolks with 2 T water and pour into flour mixture. Mix with wooden spoon until a ball begins to form. With floured hands, lightly shape dough into a ball. Wrap in plastic wrap and refrigerate for an hour.
Filling - 
In heavy bottomed pot, melt butter and add olive oil. Sautee garlic and onion for 5 mins then add rest of the vegetables cooking until partially softened. Add flour, cooking until thickened. Gradually add chicken stock until mixture bubbles and thickens. You can add more flour if you want a thicker consistency. Season with salt & pepper. Add chicken. Set aside to cool.
Preheat oven to 425 deg.
Crust -
Divide dough in half. Roll out cold pastry on a floured surface to fit whatever baking dish you are using (with straight sides to prevent spillage). I use a 9X13 pan. Mix egg whites with remaining 2 T cold water. Brush crusts with egg wash. Place one (egg wash side up) in the bottom of the baking dish. Fill with pie filling. Place second crust (egg wash side down) onto filling. Trim and pinch crust edges together. Brush top with egg wash. Cut slits in pie top to let steam release. Bake until pastry is golden brown, 35 to 45 mins. Serve immediately.