Preheat oven to 350 degrees.
Add butter to a 9x13-inch cake pan or casserole dish and melt in the oven.
Once the butter is melted, sprinkle the pecans over the butter.
In a bowl, mix flour, sugar, milk and vanilla. Stir to combine, but don't over-mix.
Pour batter over butter and pecans, do not mix.
Sprinkle brown sugar evenly over batter, do not stir.
Carefully pour the hot water over the mixture; do not stir.
Bake 30 to 35 minutes or until golden brown.
