In a Dutch oven, cook meat over medium-low heat until the mixture begins to brown. Mix in onions and celery, and continue cooking for about 5 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Arrange 2 pie crusts in a single layer on the bottom of a large roasting pan. Spread 1/2 of the meat over the pie crusts. Arrange 2 more pie crusts over the meat layer, and then spread remaining meat on top of the pastry. Top with remaining pastry. Press the pastry to the sides of the pan, and poke 8 small holes in the pastry to allow steam to escape.
Bake for 1 hour, or until dough is golden brown and the pie is hot and bubbly.
