Preheat your oven to 375°F (190°C) and lightly grease a 9×13 inch baking dish.
Prepare the apples by peeling, coring, and slicing them into ¼-inch thick slices. You want them thin enough to become tender but not so thin they disintegrate.
In a large bowl, combine the sliced apples with granulated sugar, brown sugar, 2 tablespoons flour, lemon juice, cinnamon, nutmeg, and salt. Toss until the apples are evenly coated.
Transfer the apple mixture to your prepared baking dish and spread it out evenly. Dot the surface with the 2 tablespoons of butter pieces.
Make the topping by whisking together the flour, sugar, baking powder, and salt in a medium bowl.
Cut in the cold butter using a pastry cutter or your fingertips until the mixture resembles coarse crumbs. The butter should be about pea-sized—this creates that perfect cobbler texture.
Pour the boiling water over the flour mixture and stir just until combined. The dough will seem wet, but this creates a wonderful crust.
Drop spoonfuls of the topping over the apples, covering most of the surface but allowing some gaps for the filling to bubble through.
Bake for 40-45 minutes until the topping is golden brown and the filling is bubbling around the edges.
Allow to cool for at least 15 minutes before serving warm with a scoop of vanilla ice cream if desired.