Preheat your oven to 425°F (220°C) and grease a 9x13 inch casserole dish with butter or cooking spray.

In a large mixing bowl, whisk together the chicken broth and half-and-half until well combined.

In a large skillet over medium heat, melt 3 tablespoons of butter. Add the diced onions, carrots, and celery, sauté for 5-7 minutes until tender.

Sprinkle ¼ cup of flour over the sautéed vegetables and stir well, cooking for about 1 minute. Gradually pour in the chicken broth mixture while stirring continuously.

Once the filling has thickened, gently fold in the shredded chicken and frozen peas, then transfer to the prepared casserole dish.

In a separate bowl, combine 2 cups of Bisquick, ¾ cup of buttermilk, 1 cup of shredded cheddar cheese, and 2 tablespoons of chopped parsley. Stir until just combined.

Scoop generous dollops of the biscuit dough over the filling in the casserole dish.

Place the casserole in the preheated oven and bake for 22-25 minutes until the biscuits are golden brown.

Allow it to cool for a few minutes, garnish with fresh parsley if desired, and serve warm.