Bring pie crusts to room temperature according to package directions.
In a large saucepan, combine chicken cubes, carrots, peas, and celery. Add just enough water to cover the chicken and veggies; boil for 15 minutes. Remove from heat, drain, and set aside.
In a large skillet over medium heat, sauté onions in butter until soft and translucent. Stir in flour, salt, pepper, and celery seed. Slowly whisk in chicken broth and milk. Simmer over medium-low heat until thick, stirring occasionally. Remove from heat; gently fold in chicken and veggies.
Divide filling evenly among six 4-inch ramekins.
On a well floured surface, gently unroll one pie crust at a time, using a 4 1/2-inch round biscuit cutter, cut out 6 circles.
Cover each ramekin with a pastry circle, gently pressing on top of filling; crimp edges. Make 4 small slits in the top of each pot pie to allow steam to escape. Brush the tops with milk or heavy cream.
Preheat oven to 375 degrees. Line a baking sheet with foil.
Place pies on prepared baking sheet and bake for 20 to 25 minutes or until pastry is golden brown. Cool for 5 minutes before serving.