Season the cubed duck breast fillets with salt and pepper. Heat the oil in a deep skillet over medium-high heat. Add the duck and brown evenly. Mix in 3/4 cup broth and bring to a boil. Reduce heat and simmer until the liquid is reduced by half. Add the remaining broth, turn the heat to low, cover, and simmer for another hour or until the meat is tender. Check every 20 minutes to make sure there is at least 3/4 inch of liquid in the skillet. If necessary, add more broth or water.
While the meat is cooking, heat the butter in a saucepan. Add potatoes, carrots, celery, onion, and garlic. Season with salt and pepper. Cook until the onions are translucent. Then sprinkle in flour and cook for 5 minutes while stirring. Remove from heat.
When the duck is tender, strain the liquid into the saucepan with the vegetables. Bring to a boil. Add the cooked duck and frozen peas, then remove from heat. Remove the pie crusts from the refrigerator and allow them to rest at room temperature for 20 minutes.
Preheat the oven to 375°F. Place one of the pie crusts in the bottom of an ungreased 9-inch pie pan. Next add the duck and vegetable filling. Then place the remaining crust over the top of the pie. Crimp the bottom and top crusts together. Cut a few slits into the top crust, then brush it with a beaten egg. Place the pie on a baking pan in the preheated oven for 45 minutes or until crust is golden brown.
Frozen Pot Pies There's no such thing as a quick pot pie, at least not if you want to make a good one. You can always make two pies, however, and freeze one for later. I prefer freezing unbaked pies for fresh-made flavor. Simply wrap the unbaked pie in two layers of aluminum foil and it will last for several months in your freezer. Prior to baking, thaw the pie at room temperature for 30 minutes. Then place it on a baking sheet in a preheated 425°F oven for 1 1/2 hours or until the top is golden brown and the filling is hot and bubbly.