In a large, 8 quart heavy bottomed saucepan add the carrots, celery, onion, bay leaves, pepper and parsley. Place the whole chicken on top. (See my note about cleaning the chicken). Pour over the water before placing a lid on the pot.
On high heat, bring the stock to a boil. Skim away any scum that floats to the top of the pot.
Reduce the heat to medium low and let the stock simmer gently for about 90 minutes.
Carefully remove the chicken and carrots from the pot and set aside to cool down for 20 minutes. Strain the stock through a sieve and set aside 3 cups (24 floz/720 ml) of stock for later. Discard the remaining cooked vegetables and spices.
Pick all the meat from the chicken and chop to bite size pieces. Slice the carrots and pop them into a bowl with the chicken and place into the fridge.
Wipe the mushrooms clean with a paper towel before chopping them into small pieces.
In a large saucepan over medium heat, add the butter and allow to sizzle before adding in your mushrooms.
Sautée the mushroom for 2 to 3 minutes before lowering the heat and adding the flour. Cook this ‘roux’ for roughly 2 minutes to cook the flour.
While mixing, slowly pour in reserved chicken stock, followed by the milk and cream. Stir vigorously to incorporate the liquid to your roux. Turn up the heat to medium and simmer for 3 to 5 minutes, or until thickened.
Mix in the cooked chicken, carrots and salt and pepper. Taste and add more seasoning if needed.
Transfer your cobbler filling into a large baking dish, roughly 9 x 13-inches. Once cool, cover and place in the fridge until needed. This filling can be made up to 24 hours in advance.
To Make the Buttermilk Biscuits
Preheat the oven to 375ºF (190ºC). In a large bowl, add the flour, baking powder, baking soda, salt and parsley.
Toss in the cold butter and rub in with your fingers until the mixture resembles coarse breadcrumbs.
Add the buttermilk and stir until the dough leaves the sides of the bowl. Turn out onto a floured surface and form into a ball. Pat out into a circle that is about 1-inch thick. Cut with a 3-inch round biscuit cutter. Gather and reroll any scraps.
Place the biscuits side by side on top of the cold filling. Brush the tops with egg wash.
Bake for 40 to 50 minutes, until golden brown.
Allow to cool for 20 minutes before serving. Store any leftovers in the fridge for up to 3 days. It also freezes really well for up to 8 weeks.