Begin by ensuring the oven is preheated to 200 degrees. Then, assemble garlic halves and onion quarters on a sturdy roasting tray. Clean the chicken and place it on top of the onion-garlic mix. Using olive oil, coat the chicken skin evenly, followed by a good seasoning of sea salt and black pepper.
Proceed to roast the chicken for an hour at the aforementioned temperature. Allow it to cool in the tray for an additional 10 minutes. Drain the juices extracted during the roasting into a jug by sieving the contents of the tray. Now, you can move on to shredding the chicken into sizable chunks or strips for the pie filling.
The next step involves frying the large portobello mushrooms in a non-stick pan with vegetable oil. After being cooked on high heat for a few minutes, remember to set aside the browned mushrooms.
To concoct the filling, you need to melt butter in a heating pot. After mixing in some flour, cook it for a couple of minutes on low heat. To this, you’ll add the aforementioned stock and the juices acquired from roasting. Post stirring, increase the flame to medium heat. As the sauce thickens, lower the heat and add the shredded chicken, browned mushrooms and thyme leaves into the mixture. Complete the filling preparation by introducing lemon zest and cream, all the while seasoning it once more. Ensure to thoroughly stir the mixture before taking it off the heat and transferring it into a casserole dish to cool down for a while.
As a final note, flour for dusting, an egg yolk, puff pastry (pre-rolled or block) and rosemary sprigs will be used for the garnishing portion.
Begin by lightly sprinkling a touch of flour onto a counter. Carefully extend the puff pastry sheet and tenderly lay it atop the baking dish. Ensure the pastry is securely affixed to the dish by crimping the perimeters. Softly coat the pastry with egg yolk and embellish with some sprigs of rosemary and thyme. Bake for 25-30 minutes in a 190-degree oven until the pastry becomes a deep golden hue and achieves a crispy texture. Wait for a brief period of five minutes to let it cool off slightly before it’s ready to serve.