Mix water and dry milk. Add a little bit at a time until mixture is moist but not sticky. The amount of liquid to add will vary due to moisture in the air. Grease 12 inch cast iron skillet. Press flour mixture into skillet, kneading with your knuckles as you spread biscuit mix evenly.
Place slices evenly on top of biscuits.
Mix parmesan and garlic powder and sprinkle over top. Cook on low heat for 15-25 minutes. Stick a toothpick into biscuits. When it comes out clean, the biscuits are done. Be sure cheese is bubbly.