Chicken Pot Pie Casserole

Cook and rest the chicken

Put the chicken broth and chicken in a medium saucepan and bring to a very gentle bubble, rather than a full boil, which can toughen the meat. Cook for 15 minutes or until the chicken is cooked through. Rest it for 5–10 minutes, then shred it or cut it into cubes. Pour the broth into a large measuring cup with a spout and reserve it.

Soften the vegetables

Melt the butter in a wide, high-sided skillet over medium heat. Add the onion, carrots, and celery and cook for 6 minutes, stirring frequently, until softened. Stir in the garlic, thyme, rosemary, parsley, sage, pepper, Worcestershire sauce, and Dijon mustard. Cook for another 2 minutes.

Cook the flour

Stir in the flour and cook for 2 minutes, stirring constantly.

Build the sauce

Gradually stir in 2 cups of the reserved chicken broth in small additions, stirring continuously. Add the heavy cream the same way, then add the chicken bouillon cube. Lower the heat to medium-low.

Add the potato

Peel the potato and cut it into ½-inch pieces so it can cook through. Season lightly with salt and pepper, then add it to the filling. Bring the liquid to a boil and lower it to a simmer.

Simmer until tender

Keep the potato pieces submerged and simmer gently, uncovered, for about 20 minutes. Stir regularly, lifting any ingredients that settle on the bottom. Add the remaining chicken broth in small splashes as the filling reduces and thickens; you may use all of it, depending on the consistency you prefer.

Add the chicken and peas

When the potatoes are fork tender, stir in the peas and cooked chicken. Simmer for 3 more minutes.

Fill the casserole dish

Transfer the filling to a lightly greased 9 x 13-inch casserole dish. Expect it to thicken a little as it stands.

Heat the oven

Preheat the oven to 400°F.

Combine the dry ingredients

Mix the flour, baking powder, baking soda, and salt in a large bowl.

Cut in the cold butter

Cut the cold butter into small cubes and add it to the dry ingredients. Work it in with a pastry cutter or the back of a fork until the mixture forms coarse crumbs.

Add the milk and sour cream

Use a silicone spatula to stir in the milk and sour cream gently, just until combined. Keep the dough crumbly and avoid overmixing.

Cover with biscuit dough

Place small handfuls of dough over the filling, covering most of its surface. Leave the pieces rustic rather than smoothing them into an even sheet.

Brush on the egg wash

Whisk the egg with the milk, then use a pastry brush to apply a light coating over the biscuit dough.

Bake uncovered

Bake without a cover for 30 minutes. The topping should be golden, the filling hot and bubbling, and a toothpick inserted into the biscuit topping should come out clean.

Rest before serving

Let the casserole cool for 5 minutes before serving.