HEAT OVEN to 350F/177C for chicken (unless using a pre-cooked rotisserie chicken). Line a sheet pan with foil or parchment paper for easy clean up.
COOK CHICKEN: Place chicken on prepared sheet pan, skin side up. Rub with oil, sprinkle with salt and black pepper, roast for 35-40 minutes until done (165F/74C). When chicken is cool enough to handle, take skin off, remove meat from bones and dice into chunks (e.g. 1.5 inches/3.8cm). You will have 3-4 cups. Note 1 for shortcut.
COOK VEGETABLES: Blanch (boil) vegetables (except parsley) in a pot of boiling water for 2 minutes. Drain and set aside. Alternatively, blanch in microwave for 1-2 minutes, covered, with a tablespoon of water.
MAKE PASTRY CRUST: Mix flour, baking powder and salt in bowl of a food processor fitted with metal blade. Add butter and shortening. Use your fingers to make sure each piece is covered in flour (watch your fingers! better yet, use a spoon). Pulse processor 10 times. Add butter and shortening. With motor running, start adding 1/2 cup ice water and process just until dough is moistened and comes together (you may need a bit more ice water). Place dough on floured board and knead quickly into a ball. Wrap in plastic and then let it rest in fridge for 30 minutes.
MAKE SAUCE: In a medium saucepan, heat stock with bouillon cubes until cubes are dissolved. In a large pot, melt butter and sauté onions over medium heat until translucent, 10 minutes. Mix in flour and cook for 2 minutes, stirring constantly. Add the hot stock, whisking to combine well. Cook 3-4 minutes until sauce is thickened. Add 2 teaspoons salt (or to taste), 1/2 teaspoon pepper. and cream. Add cubed chicken, blanched vegetables, parsley and peas to the sauce. Stir.
Preheat oven to 375F/190C to bake pot pies.
ASSEMBLE: Divide chicken mixture evenly among 4 ovenproof bowls. Divide the dough in 4 pieces and roll each piece in an 8 inch circle. Dough should be about 1/4 inch thick. Spray some oil on your fingers and brush them along the outside edges of each bowl (and down the side about 1 inch/2.5cm). This will make clean up much easier. For each pot pie, place the dough on the filled bowl, mold or crimp over the sides and trim to 1/2 inch overhang. (At this point, you can put the individual pies in the fridge covered. Note 5.)
BAKE: Brush the dough with egg wash and make 3 slits on the top. Decorate with bits of extra dough if you like. Place pot pies on a foil-lined baking sheet and bake for 1 hour until golden brown.