Adjust the oven rack to the middle position and heat the oven to 350 degrees. Grease and flour a 9 x 13, broiler safe baking pan (Do not use Pyrex). Whisk together the flour, baking powder, and salt in a large bowl. Set aside. Heat the butter and the milk in a small saucepan over medium heat until melted. Stir in the vanilla.
In a medium bowl, beat together the eggs and granulated sugar with an electric mixer on medium high until pale and thick, about 6 minutes. Fold half of the flour mixture into the egg mixture, then stir in 1/2 of the milk mixture, stir the other half of the flour mixture into the egg mixture, then stir in the other 1/2 of the milk mixture.
Pour the batter into the prepared pan and bake until a toothpick inserted in the center of the cake comes out clean, 30-35 minutes. Let cool slightly in the pan, about 10 minutes. Heat the broiler.
For the topping:
In a medium bowl, melt the 9 Tbls. butter in the microwave. Add the brown sugar, evaporated milk, and the coconut. Spread the mixture on top of the cake.
Place the cake back in the oven and broil until the topping is bubbling and starts to brown, about 3-4 minutes. Serve Warm.