In a large pot, add a whole chicken, chopped brown onion, bay leaves, fresh thyme, diced carrot, and whole cloves. Cover with water and bring to a boil over medium-high heat, then reduce to a simmer. Cook for about 1 hour, or until the chicken is tender and cooked through, skimming off any foam. Once ready, carefully remove the chicken and reserve the flavorful stock.

Allow the chicken to cool slightly before shredding the meat into bite-sized pieces using two forks. Set aside the shredded chicken to chill. Return the chicken carcass to the pot with the remaining stock and simmer for an additional hour to deepen the flavor. Strain the stock into a separate container and refrigerate until ready to use.

In a large skillet, melt butter over medium heat and sauté finely chopped onion, chopped leeks, and diced carrot for around 20 minutes, stirring frequently. When the vegetables are soft and fragrant, add white wine and let it simmer for a couple of minutes. Whisk together plain flour and cream before adding to the skillet, followed by the reserved stock, Dijon mustard, and grated Parmesan. Stir until thickened and remove from heat.

Gently fold the shredded chicken into the creamy filling mixture, ensuring everything is evenly coated. Season to taste with sea salt and ground pepper. Allow the filling to cool completely before transferring it to the refrigerator.

Roll out the butter puff pastry on a lightly floured surface to fit a 25cm pie dish. Carefully line the dish with one circle of pastry, ensuring there are no air pockets. Fill the pastry shell generously with the chilled chicken and leek filling, then roll out another pastry circle to cover the top. Seal the edges by crimping with your fingers or a fork, and cut a few slits in the top for steam to escape.

Refrigerate the assembled Chicken Leek and Thyme Pie for about 30 minutes to help the pastry firm up. Meanwhile, preheat your oven to 180°C (350°F). Once chilled, brush the top with the whisked egg for a beautiful golden finish. Bake for 55-60 minutes, or until the pastry is puffed and golden brown. Let it cool for about 5 minutes before slicing and serving.