Step 1: Preheat the Oven
Preheat your oven to 350°F (175°C) and lightly grease a 9×9-inch baking dish or an 8×8-inch dish for a thicker cobbler. Set the dish aside.

Step 2: Prepare the Cobbler Batter
In a medium mixing bowl, whisk together the flour, baking powder, salt, ground cinnamon, and granulated sugar. Once combined, stir in the milk and melted butter until you have a smooth batter. It will resemble pancake batter in consistency. Pour the batter into the prepared baking dish, spreading it evenly.

Step 3: Add the Cinnamon Sugar Topping
In a small bowl, mix together the granulated sugar, brown sugar, and ground cinnamon for the topping. Sprinkle this mixture evenly over the cobbler batter. Make sure to cover the surface completely for that signature snickerdoodle flavor.

Step 4: Prepare the Gooey Sauce
In another small bowl or measuring cup, combine the hot water and melted butter. Slowly and carefully pour this liquid mixture over the cobbler batter and cinnamon sugar topping. Do not stir; the liquid will sit on top, and as it bakes, it will sink to the bottom to create the gooey sauce layer.

Step 5: Bake the Cobbler
Place the dish in the preheated oven and bake for 35-40 minutes, or until the top is golden brown and set. The cobbler may still jiggle slightly due to the sauce underneath, but the top should be firm and crisp.

Step 6: Cool and Serve
Let the cobbler cool for about 10 minutes to allow the layers to settle. Serve warm with a scoop of vanilla ice cream or a dollop of whipped cream for the ultimate dessert experience.