Phase 1: Prepare the Creamy Chicken Filling

1. Cook the Chicken (if using raw): Season the cubed chicken generously with about 1/2 teaspoon salt and 1/4 teaspoon pepper. Heat 1 tablespoon of olive oil or butter in a large Dutch oven or oven-safe skillet over medium-high heat. Add the chicken in a single layer (work in batches if necessary to avoid crowding the pan). Cook for 5-7 minutes, turning occasionally, until lightly browned and just cooked through. Remove the chicken from the pot with a slotted spoon and set aside on a plate. Don’t worry if it’s not cooked completely; it will finish cooking in the sauce.
2. Sauté the Aromatics: Reduce the heat to medium. Add the 4 tablespoons of unsalted butter to the same pot. Once melted, add the chopped onion, diced carrots, and diced celery. Cook, stirring frequently, for about 8-10 minutes, until the vegetables soften and the onion becomes translucent. Don’t rush this step; sweating the vegetables properly builds a crucial layer of flavor.
3. Add Garlic and Herbs: Stir in the minced garlic and chopped fresh thyme (or dried thyme). Cook for about 1 minute more, until fragrant. Be careful not to burn the garlic.
4. Create the Roux: Sprinkle the 1/3 cup of all-purpose flour evenly over the cooked vegetables. Stir constantly and cook for 1-2 minutes. This cooks out the raw flour taste and forms a paste (roux) that will thicken the sauce. The mixture will look a bit clumpy or pasty.
5. Build the Sauce: Slowly pour in the chicken broth, whisking constantly as you add it. Start with about half a cup, whisking vigorously to incorporate the flour mixture smoothly, ensuring there are no lumps. Gradually add the remaining broth, continuing to whisk until smooth.
6. Add Dairy and Simmer: Pour in the whole milk or heavy cream, whisking to combine. Bring the mixture to a gentle simmer, stirring occasionally. Let it simmer for 5-8 minutes, allowing the sauce to thicken enough to coat the back of a spoon. If the sauce seems too thick, you can add a splash more broth or milk. If too thin, let it simmer a bit longer (it will thicken more as it cools slightly and bakes).
7. Season and Add Remaining Ingredients: Stir in the remaining 1 teaspoon of salt and 3/4 teaspoon of black pepper (adjust to your taste). Taste the sauce and adjust seasonings if needed. Stir in the cooked chicken (along with any accumulated juices from the plate), the frozen peas, and the chopped fresh parsley. If using pre-cooked/rotisserie chicken, add it now. Stir everything together until well combined.
8. Transfer to Baking Dish (if needed): If your Dutch oven or skillet is not oven-safe or if you prefer a casserole dish, carefully pour the chicken filling into a 9×13 inch baking dish (or a similar 3-quart capacity dish). Preheat your oven to 400°F (200°C).

Phase 2: Make the Homestyle Biscuits

(While the filling rests slightly or simmers, prepare the biscuit dough. Work quickly to keep the butter cold.)

1. Combine Dry Ingredients: In a large bowl, whisk together the 2 cups of all-purpose flour, 1 tablespoon baking powder, 1 teaspoon salt, and optional 1 teaspoon sugar.
2. Cut in the Butter: Add the cold, cubed butter to the flour mixture. Use a pastry blender, two knives, or your fingertips to cut the butter into the flour until the mixture resembles coarse meal with some pea-sized pieces of butter remaining. Work quickly to prevent the butter from melting. Tip: Some visible butter pieces are good – they create flakiness!
3. Add Milk: Create a well in the center of the flour/butter mixture. Pour in the 3/4 cup of cold milk or buttermilk all at once. Use a fork or spatula to stir gently until the dough just comes together. It will look shaggy – do NOT overmix! Overmixing develops gluten and makes the biscuits tough.
4. Turn Out and Knead Briefly (Optional but Recommended): Turn the shaggy dough out onto a lightly floured surface. Gently bring it together and knead it very briefly – just 5-6 turns – to make it cohesive. Pat the dough out into a rectangle about 1/2 to 3/4 inch thick. For extra flaky layers (optional): Fold the dough like a letter (in thirds), gently pat it out again, and repeat the fold once more.
5. Cut the Biscuits: Use a 2.5 or 3-inch round biscuit cutter (dip the cutter in flour between cuts to prevent sticking) to cut out biscuits. Push the cutter straight down – don’t twist, as twisting can seal the edges and prevent rising. You should get about 8-10 biscuits. Gently re-pat the scraps together to cut additional biscuits, handling the dough as little as possible.

Phase 3: Assemble and Bake

1. Top the Filling: Arrange the cut biscuit dough rounds evenly over the hot chicken filling in the Dutch oven or baking dish. They should be close together but ideally not overlapping too much, allowing steam to escape.
2. Optional Brush: For golden-brown tops, you can lightly brush the tops of the biscuits with melted butter or a little milk/cream.
3. Bake: Carefully place the Dutch oven or baking dish into the preheated 400°F (200°C) oven. Bake for 18-25 minutes, or until the filling is bubbling vigorously around the edges and the biscuits are tall, golden brown, and cooked through. If the biscuits brown too quickly before the filling is hot enough, you can loosely tent the dish with foil.
4. Rest: Once baked, remove the dish from the oven and let it rest for 5-10 minutes before serving. This allows the filling to thicken slightly more and prevents burnt tongues!
5. Garnish and Serve: Garnish generously with fresh chopped parsley just before serving for a pop of color and freshness.