Melt butter over medium heat in a large pot. Saute the onions in the butter for 3-5 minutes or until the onions become translucent.
Add the half-and-half, chicken broth, mixed vegetables, chicken, and seasoning. Stir and cook for 5 minutes.
Whisk together cornstarch and water. Add to the chicken pot pie filling and stir well. Cook for 5 minutes. Remove the filling from the heat source.
Divide dough for pie crust into thirds. Roll ⅓ out on a lightly floured surface into a circle. Place pie dough in pie pan. Place pie pan on a rimmed baking sheet.
Carefully pour the chicken pot pie filling into the pie pan.
Roll out ⅓ of the pie crust into a circle. Place crust on top of pie filling. Trim excess pie crust. Take the excess and roll into a long rope. Place the rope around the top ledge of the chicken pot pie. Using your fingers, pinch the rope to make scallop shapes. Slit the top pie crust with a few "Xs" to allow steam to escape.
Bake for 30 - 40 minutes or until the crust is golden brown. Allow the chicken pot pie to cool for 10 minutes before serving.
Nutrition information does not include values for the pie crust.