Pat chicken dry with paper towels and season with salt, pepper & onion powder on both sides. Heat 2 Tbls. oil in large Dutch oven over high heat until just smoking. Cook chicken until well browned, about 2.5 minutes on each side. Add broth and bring to boil. Cover and simmer over low heat until chicken is cooked through, 6-8 minutes. Transfer chicken to large plate and strain broth into bowl.
Melt butter with remaining 2 Tbls. oil in now-empty Dutch oven over med-high heat. Cook onion, carrots, celery and 1/2 t. salt until lightly browned and softened, 8-10 minutes. Reduce heat to medium, and add flour, and cook 1 minute. Whisk in reserved broth and cream and simmer until sauce thickens, about 10 mins.
Meanwhile, using 2 forks, shred chicken into bite-sized pieces. Off heat, add the chicken and lemon juice to sauce and season with salt and pepper. Transfer filling to large bowl and cool until just warm. Cover with plastic wrap and refrigerate until well chilled, about 1 hour. Stir peas into filling and divide mixture among 6 disposable aluminum loaf pans.
Unwrap and unroll pie crusts onto lightly floured counter. "Glue" 2 crusts together using 1 beaten egg and brushing the bottom crust with egg. Use a disposable aluminum pan turned upside down to cut out 2 pastry toppings from double-thick pie dough. Repeat with 4 more pie crusts. Top with pasty and use fork to seal edges. Using paring knife, make 3 steam vents in each crust.
Tightly wrap each loaf pan in 2 layers of plastic wrap and 1 layer of aluminum foil. Freeze for up to 2 months.
When ready to serve: Adjust oven rack to middle position and heat over to 400 degrees. Unwrap frozen pot pies and arrange on rimmed baking sheet. Brush crusts with egg, cover with foil, and bake 40 mins. Uncover and bake until crusts are golden brown, about 35 mins. Let pot pie rest 10 minutes before serving.
Notes:This recipe is a double batch from the original because I figured it's the same trouble to make 3 tins as it is to make 6. Since these go in the freezer, they stay great and are nice to always have on hand to pop in the oven! One hint - you can't eat these as soon as you are done making them because they need to freeze for a couple of hours, so make them early if you want to have them for dinner! Enjoy :)