Preheat oven to 350 degrees.
Melt butter in a 9x13 inch pan.
In a mixing bowl, combine flour, sugar, milk, vanilla extract, and cinnamon.
Stir to combine, but do not over-mix.
Pour the batter over the melted butter.
Sprinkle brown sugar over the top of the batter.
Carefully pour hot water over the butter and batter. Do not stir.
Bake for 30 to 35 minutes until golden brown.