Melt the butter in a saucepan and add the flour. Stir until a paste with lumps forms. Add the milk and stir constantly with a whisk. When the mixture starts to thicken, add the chicken and vegetable broth, continuing to stir until the desired consistency is reached. Add the chicken and vegetables. Season. Pour into a broken pie crust and cover with another crust. Bake in the oven at 400 F for 30 to 40 minutes.