Follow these simple steps to create your delicious Chicken Pot Pie:

1. Cook the Chicken: In a large pot, boil the chicken breasts in salted water for 15-20 minutes. Remove, let cool, and dice into bite-sized pieces.
2. Sauté the Vegetables: In a large skillet, melt the butter over medium heat. Add onions and garlic, cooking until softened (about 3-5 minutes).
3. Add Vegetables: Stir in the carrots, potatoes, peas, corn, thyme, rosemary, salt, and pepper. Cook for 5-7 minutes until the vegetables are slightly tender.
4. Prepare the Sauce: Pour in the chicken broth and heavy cream, stirring well to combine. Cook until the mixture thickens (about 5-10 minutes).
5. Combine Fillings: Remove from heat and stir in the diced chicken. Mix until all ingredients are well coated in the sauce.
6. Preheat the Oven: Preheat your oven to 425°F (220°C).
7. Assemble the Pie: Pour the chicken filling into a pie dish. Cover with the pie crust, pinching the edges to seal. Cut slits in the top for venting, then brush with the beaten egg.
8. Bake: Place the pie in the preheated oven and bake for 40-45 minutes, or until the crust is golden brown.
9. Cool: Allow the pie to cool for about 10-15 minutes before slicing. This will help the filling set slightly.