Begin by preheating your oven to 375℉. Then, heat up your cast iron over medium heat, and bring 2 cups of water to a boil in your saucepan.As your pan, water, and oven heat up, dice the onion, celery, and potato. Set aside. To begin the sauce, in a medium-sized mixing bowl whisk together the flour, onion powder, garlic powder, garlic salt, pepper, and milk.
Melt 1 tbsp of butter in the hot cast iron, and add the diced potatoes and minced garlic. Cook for about 5-10 minutes until the potatoes are browned and tender when pierced with a fork.
While you cook the potatoes, add the chicken bouillon for the sauce to the boiling water and whisk until dissolved. Add the milk/dry ingredient mixture you've already mixed together in step 2. Stir consistently until thickened (about 3 minutes).
While the sauce thickens add the diced onion and celery to the cast iron once the potatoes are browned. Stir occasionally and cook for about 5 minutes. Then add the bag of frozen veggies and cook for about 5 more minutes until everything is warmed and softened. Lastly, add the shredded chicken.
Pour the thickened sauce into the cast iron and stir until its all combined. Take off heat and set aside.
In the same medium-sized mixing bowl you used for the flour mixture for the sauce, whisk together the whole wheat flour, all-purpose flour, baking soda, baking powder, sugar, and salt for the biscuit crust. Cut the butter into small pieces and, using a pastry cutter, mix together until you have course crumbs. Add the greek yogurt, milk, and egg. Stir to combine. The mixture will be sticky and fairly wet. Top the filling and sauce mixture with roughly 6 dollops of the biscuit mixture. Spread the dollops slightly so that they are touching but does not have to cover the filling/sauce mixture uniformly.
Bake for 30-35 minutes until the biscuit crust is browned and the filling/sauce is bubbly. Enjoy!
