In a big pot, start by bringing two cups of water to a boil. Add the chicken breasts and reduce the heat to a simmer. Cook for 15 minutes, or until the chicken is fully cooked.

Remove the chicken, shred it, and set aside. In the same pot, toss in the carrots, celery, and onion, and cook them until they begin to soften—about 5 minutes.

In a separate large skillet, melt the butter over medium heat. Stir in the cornstarch and flour to create a smooth roux. Gradually add the heavy whipping cream, stirring continuously until the sauce thickens.

Add the chicken bouillon, black pepper, and frozen peas, and stir. Finally, add the shredded chicken and vegetables to the sauce, ensuring everything is well-coated.

Mix the flour and salt together in a large mixing dish. Cut in the chilled shortening using a pastry cutter or your hands until the mixture resembles coarse crumbs.

Slowly add cold water, one tablespoon at a time, mixing until the dough holds together. Divide the dough into two, and roll out one portion to fit a 9-inch pie dish. Save the other half for the top crust.

Preheat your oven to 375°F (190°C). Pour the chicken and vegetable filling into the bottom crust. Spread the remaining dough to a second thickness and cover. To let steam out, seal the edges and make a few vents in the top.

Bake your chicken pot pie for 40-45 minutes or until the crust is golden brown. Let it cool for 10 minutes before serving.