01 - Preheat the oven to 350°F (177°C). Pour the melted unsalted butter into a 9x13 inch baking pan and spread evenly to coat the bottom.
02 - In a large mixing bowl, whisk together whole milk, vanilla extract, and 1 1/2 cups granulated sugar. Add all-purpose flour, baking powder, salt, and 2 teaspoons ground cinnamon. Whisk until the batter is just incorporated and smooth.
03 - Gently spoon the batter over the melted butter in the pan, taking care not to stir or mix. Evenly sprinkle the packed brown sugar over the surface of the batter.
04 - Carefully pour the hot water evenly over the brown sugar and batter. Do not stir.
05 - Place the pan in the preheated oven and bake for 30 to 35 minutes, or until the top is golden brown and the cobbler is mostly set with a gooey texture underneath.
06 - In a small bowl, combine 1/4 cup granulated sugar with 1/2 teaspoon ground cinnamon. Mix thoroughly.
07 - As soon as the cobbler is removed from the oven, sprinkle the cinnamon sugar topping evenly over the hot surface. Allow to cool slightly before portioning and serving.