In a large saucepan, add apples, 2 tablespoons butter, corn starch, ⅓ cup granulated sugar, brown sugar, 1 teaspoon cinnamon, and salt. Stir to combine and then slowly stir in water.
Bring to a low boil and cook, stirring occasionally, until tender (about 15 minutes). Remove from heat and set aside.
Preheat oven to 375°F. Grease a 10-inch cast iron skillet with 1 tablespoon butter. Set aside.
Using your hands or a rolling pin, flatten each biscuit into a 4-inch round.
Place a couple of tablespoons of apple filling in center of biscuit. Wrap dough around apple filling, pressing edges to seal.
Place seam side down in prepared iron skillet, leaving a little room for spreading. Continue until all biscuits have been filled.
In a small bowl, whisk together ⅓ cup granulated sugar and 1 teaspoon cinnamon; set aside.
Melt remaining 4 tablespoons butter. Pour evenly on top of biscuits. Sprinkle top of biscuits with spiced sugar.
Bake for 16 to 18 minutes, or until golden brown. Let rest 5 minutes and serve warm.
