Combine the onion, celery, garlic, broth, pepper and squirrel in a large pot and bring to a boil; simmer until meat is very tender and easily removed from bones. Debone the meat and set aside; researve 1 cup cooking liquid.
Fit the bottom crust into a pie pan.
Combine the meat, vegetables reserved broth and cornstarch in a large bowl and mix well; spoon the mixture into the pie shell. Top with the second crust, press the edges to seal and cut vents in the top for steam to escape. Bake at 350 degrees until crust is browned, about 1 hour.