1. Preheat Oven: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish.
2. Cook Pasta: Boil penne pasta according to package instructions until al dente. Drain and set aside.
3. Prepare the Sauce Base:
   • In a large skillet, melt butter over medium heat. Add diced onion, carrots, and celery, cooking until softened (5-7 minutes).
   • Add garlic and cook for 1-2 minutes until fragrant.
   • Sprinkle flour over the vegetables and stir well. Cook for 1-2 minutes to remove the raw flour taste.
4. Make the Sauce:
   • Gradually whisk in chicken broth and milk until smooth. Bring to a simmer, stirring frequently, until the mixture thickens.
   • Stir in chicken, peas, thyme, salt, and pepper. Cook for 2-3 minutes.
5. Combine and Transfer: Mix the cooked pasta into the skillet until evenly coated. Transfer the mixture to the prepared baking dish, spreading it evenly.
6. Top with Puff Pastry: Roll out the puff pastry to fit the baking dish. Lay it over the pasta mixture and brush with beaten egg for a golden finish.
7. Bake: Place the dish in the oven and bake for 25-30 minutes, or until the puff pastry is golden brown and the filling is bubbling.
8. Serve: Let the dish cool for a few minutes before slicing and serving.

Prep Time: 20 minutes
Cooking Time: 40-45 minutes
Total Time: 60-65 minutes
Servings: 6
Calories: ~450 per serving

Tips:

• Use rotisserie or leftover chicken to save time.
• Add mushrooms or green beans for extra texture and flavor.
• Serve with a crisp side salad or roasted vegetables for a balanced meal.