Melt 6 T. of butter over medium heat in a saucepan. When it starts to bubble, whisk in 6 T. of flour. Cook until golden, whisking constantly, about 3-5 minutes. Whisk in 4 cups of chicken broth, stirring fast to avoid lumps. Cook until thickened, about 5 minutes, then remove from heat.
Preferably in a cast iron skillet, melt 3 T. of butter over medium heat. Cook one chopped onion five minutes, then stir in one cup chopped carrot. Cook another five minutes. During cooking, stir in 2 tsp. poultry seasoning, 1 tsp. salt, 1/2 tsp. pepper. Remove the meat from one rotisserie chicken and chop. (Or cook your own chicken. You will need around two cups at least. ) Turn off heat and stir in one cup of peas, the chicken, and the gravy.
At this point, if using the cast iron pan, just top with a pre made pie crust. Or, you can spoon the mixture into a pie plate and put crust on top. Bake at 425 for 20-25 minutes. Let cool 10 minutes before serving.