CHICKEN AND MUSHROOM PIE

Steps:

• Preheat the oven to 425 degrees F (220 degrees C). Grease a 9-inch pie dish.
• Melt butter in a saucepan over medium-high heat. Whisk in flour. Continue to whisk until the flour combines thoroughly with butter, 2 to 3 minutes. Add milk, a little at a time, whisking to prevent burning, until thickened. Keep stirring until it begins to boil. Reduce heat and allow to simmer.
• Heat oil in a large pan over medium heat. Add chicken and cook and stir until no longer pink in the centers, 7 to 10 minutes. Add mushrooms, onion, celery, carrot, rosemary, oregano, garlic, salt, and pepper and cook until they begin to soften, about 10 minutes. Add the milk mixture and stir thoroughly. Simmer for an additional 5 to 10 minutes. Stir in Cheddar cheese and mustard until cheese is melted.
• Lay 1 sheet of pie pastry in the prepared pie dish. Add the chicken mixture to the dish. Cover pie with remaining pastry, pinching the sides together and trimming off any excess dough. Cut a slit in the center of the pie for ventilation.
• Bake in the preheated oven until golden brown, 20 to 30 minutes.