01 -
Preheat oven to 350°F. Place unsalted butter in a 9x13 inch baking dish and let it melt in the preheating oven.
02 -
Combine all-purpose flour, 1 cup granulated sugar, baking powder, salt, ground cinnamon, whole milk, and vanilla extract in a medium bowl. Mix until a smooth batter forms.
03 -
Remove baking dish from oven when butter is fully melted. Pour batter evenly over melted butter. Do not stir.
04 -
In a small bowl, mix 1/2 cup granulated sugar with 1 tablespoon ground cinnamon until thoroughly blended.
05 -
Sprinkle cinnamon-sugar mixture evenly over batter in baking dish. Pour hot water slowly over the surface, avoiding stirring.
06 -
Bake uncovered at 350°F for 40 to 45 minutes, until surface is golden brown and filling is bubbling.