If your pie crust is frozen, make sure to defrost it.
Preheat the oven to 375 degrees F.
Boil water in a large pot and add the diced potatoes and chopped broccoli. Cook for about 12 minutes. (Drain and set aside when done)
While the potatoes and broccoli cook, cut the chicken into bite sized pieces. In a large frying pan over medium heat, add the chicken and some olive oil. Top the chicken with 1/2 teaspoon dried rosemary, 1/2 teaspoon dried thyme, 1/2 teaspoon garlic powder, and 1/2 teaspoon onion powder. Cook for 5-7 mins, mixing every so often until the chicken is cooked through, then set it aside.
In a large sauce pan over medium heat, melt the 3 Tablespoons of butter. Add 1/2 cup of flour and mix with a whisk or fork until it all clumps together. Add 1 cup of milk and whisk until the mixture thickens. Add another cup of milk and whisk again. Add 1/2 cup of milk and whisk. The sauce should be thick. If it is too thick add a little bit more milk. Remove the pan from heat. Add 1/4 teaspoon nutmeg, 1/4 teaspoon dried rosemary, 1/4 teaspoon dried thyme, 1 1/2 teaspoons salt, 1/4 teaspoon ground black pepper, and 1/4 teaspoon garlic powder to the sauce and mix. Add the cooked chicken, boiled potatoes, boiled broccoli, and frozen mixed veggies to the sauce and mix.
Place one of the pie crusts into a 9 inch deep dish pie pan thats 1.5- 2 inches deep. Push the top edges of the crust down into the dish with a fork. Pour the chicken and veggie pot pie mixture into the crust. Top with the second pie crust. Crimp the pie crust down, to connect it to the pie crust already in the dish to seal the edges. Use a knife to gently cut a few slits into the top of the pot pie. Bake for 45 minutes, until golden. Let cool for 10-20 minutes before serving.