01 -
Turn oven on to 375°F (190°C). Lightly grease a 9x13 baking pan.
02 -
Cook penne in boiling water till just firm. Drain well and keep off to the side.
03 -
In a big pan, melt butter over medium heat. Toss in onion, carrots, and celery. Cook 5-7 minutes until soft. Mix in garlic and cook another minute.
04 -
Sprinkle flour on the veggies and stir. Let it cook for 1-2 minutes so the flour taste goes away.
05 -
Slowly whisk in chicken broth and milk, stirring all the time until smooth. Let it bubble until thick enough to coat a spoon’s back.
06 -
Add chicken, peas, thyme, salt, and pepper. Let it gently bubble for a little bit so flavors blend.
07 -
Put the cooked pasta in the pan and fold it with the sauce until everything’s mixed.
08 -
Spoon the pasta mix into the greased dish. Put the puff pastry sheet on top, trimming if needed and folding edges in nicely.
09 -
Paint the puff pastry with the beaten egg so it browns nicely.
10 -
Pop it in the oven for 25-30 minutes until the pastry is golden and the filling bubbles.
11 -
Give it 5-10 minutes to cool before serving so it firms up.