Skip this section if using precooked chicken. Whether baking or using an air fryer, the chicken can be made a day ahead and stored in an airtight container in the refrigerator until needed.

Pat the chicken dry with paper towels. Rub with olive oil and season with salt and pepper. Lightly grease the air fryer basket with vegetable cooking spray. Place 2 to 4 chicken breasts (cook in batches if needed) skin side down in the air fryer. Set temperature to 350 degrees. Cook for 20 minutes flipping and rotating the chicken halfway through. Continue cooking until the chicken registers 160 degrees, about 2 to 4 minutes more. Remove to a plate and tent with foil for 10 minutes. Remove the meat from the bone and discard the skin. Chop and set aside. Repeat with remaining chicken.

Preheat oven to 350 degrees F. Rub the chicken breasts with olive oil. Season with salt and pepper. Roast the chicken for 35 to 40 minutes or until cooked through. Remove from the oven and tent with foil for 15 minutes or until cool enough to handle. Remove the meat from the bones and discard the skin. Chop and set aside.

Preheat oven to 350 degrees F. Lightly grease a 13x9-inch casserole dish with vegetable cooking spray. Set aside.

Pour 1 cup of the chicken stock into a 2 cup measuring cup. Heat in the microwave for 2 minutes or until the stock is hot. Add the bouillon cubes and stir to dissolve. Set aside.

Melt the butter in a large pot or Dutch oven over medium-high heat. Add the onions, celery, carrots and mushrooms. Season lightly with salt and pepper. Cook, stirring frequently, until the onion is soft and the mushrooms release their moisture and then evaporates, about 10 minutes. Add the flour and thyme leaves and stir until the vegetables are coated. Continue cooking and stirring for 3 to 4 minutes or until a light brown fond forms on the bottom of the pot.

Pour in the hot chicken stock with bouillon into the veggies scraping up the bottom of the pan to remove any crusty bits. Add all remaining stock and continue cooking until the sauce thickens, about 3 minutes more. Stir in the heavy cream until blended. Gently fold in the peas, parsley and the diced chicken. Remove from the heat. Check the seasoning and add salt as needed. Pour the chicken mixture into the prepared casserole. Place the casserole dish on a foil lined baking sheet (in case it bubbles over) and set aside.

Whisk together the flour, baking powder, salt and pepper in a medium bowl. Add the sliced butter and using a pastry cutter blend the butter into the flour until it resembles coarse meal. Add the milk, thyme and parsley to the flour mixture. Gently stir with a spatula until a sticky dough forms. Don’t over-mix.

Using a medium size ice cream scoop drop balls of dough over the filling. You should have about 14 biscuit mounds. Brush the doughy mounds with milk. Bake until the biscuits are golden brown and the filling is bubbly, about 55 to 60 minutes. Allow the casserole to rest for 15 minutes before serving.