Cook Chicken: Season chicken with salt and pepper. Add the chicken to a saucepan and cover with water. Bring it to a low boil, reduce to simmer and cook until chicken is just barely cooked through (8-12 minutes). Remove chicken to a plate to rest before chopping into bite-size pieces. Reserve about 1 3/4 cups of the water in a measuring cup and discard the rest.

Chicken Pot Pie Filling: In a large cast iron skillet (at least 12’’x2’’), add onions, celery, and butter then cook for a few minutes, until soft and translucent. Stir in the flour, salt, pepper, garlic powder, rosemary, thyme, celery seed, and bouillon paste. Gradually stir in reserved water, then milk. Simmer over medium-low heat until thickened.

Add chopped chicken and frozen vegetables. Taste and season with more salt, pepper, bouillon, spices etc, as needed. (Pour into a casserole dish if you don't have an oven-safe skillet to add biscuits and bake).

Preheat oven to 400 degrees F.

Make Biscuits: Stir flour, baking powder, and salt together. Add butter and cut in with forks or a pastry blender until there are no large pieces. Stir in milk to form a dough. Pour dough onto a floured surface and shape into a rectangle about 3/4 inch thick. Use a round biscuit cutter (or drinking glass, or simply cut the dough into square instead of circles) to cut about 8 large biscuits.

Place biscuits directly on the surface of the chicken filling mixture in the pot.

Bake for about 25 minutes, or until the biscuits are cooked through and golden.