4 tablespoons butter
1/4 cup onion, chopped
1/4 cup celery, chopped
1/4 cup carrot, chopped
1/4 teaspoon salt
2 tablespoons flour
2 cups milk
1/2 cup heavy cream
1 chicken stock cube
2 cups chicken, cooked and chopped
1/2 cup frozen peas
1/2 teaspoon fresh thyme plus more for garnish if desired
1 sheet frozen puff pastry
1 egg, beaten slightly with a fork
Preheat oven to 200 degrees. Allow puff pastry to thaw at room temperature.
In a large pot, melt butter over medium high heat.
Add onion, celery, carrot, and salt and sauté until onions are translucent and vegetables start to get tender.
Sprinkle flour over vegetables and cook for 1-2 minutes.
Gradually whisk in milk, heavy cream and stock cube, and bring to a slow boil.
Simmer gently over medium heat until sauce begins to thicken (5 minutes). Turn heat to low, and add chicken, peas and thyme.
Pour chicken mixture into baking dish.
Cut puff pastry into 12 equal strips. Lay puff pastry strips over chicken mixture, weaving it together to form a lattice pattern.
Using a pastry brush, brush egg onto the top of the puff pastry.
Bake for 30-35 minutes. The puff pastry will be a deep golden brown colour. Cool for 5 minutes before serving.