Place the butter in the freezer for 10-15 minutes to chill.
Cut the butter up into cubes and place in a food processor with the flour, baking powder, and salt. Blend for 10-15 seconds until you have a crumbly mixture.
Add the sourdough discard and milk and pulse again until combined about 20-30 seconds.
Once mixed, place the dough on a lightly floured surface. Roll the dough and fold it into thirds. Roll out the dough into a thick rectangle.
Cover and set the dough aside in the fridge.
Preheat the oven to 425℉ degrees.
Melt 4 tablespoons of butter in a cast iron skillet. Sautee the diced onion and minced garlic until softened.
Add ¼ cup flour and stir. Cook for about 2 minutes.
Slowly add in 1 cup milk & 1 ½ cup chicken broth. Season with all the seasonings and let simmer for 5-10 minutes until slightly thickened.
Mix in shredded, cooked chicken and frozen vegetables.
Cut sourdough biscuit dough into 8 rounds and place on top. Brush the tops with milk if desired.
Bake at 425℉ for about 25 minutes or until the tops of the biscuits are golden brown and the filling is bubbly.
