Preheat oven to 350 degrees.
In a large mixing bowl, blend pineapple, eggs, water, and oil together.
Add the cake mix. Mix well.
Pour into a greased 9x13 cake pan.
Bake at 350 degrees for 35 to 40 minutes, until done.
2While the cake is baking make the topping.
3FOR THE TOPPING:
In a medium saucepan, melt the butter on medium heat, whisking frequently. Continue to cook the butter, letting it stay longer on the heat to brown it. Watch carefully as lightly browned specks begin to form at the bottom of the pan. Smell the butter; it should have a nutty aroma. It's very easy to overcook browned butter and go from brown to burnt.
Quickly stir in the pineapple juice and the condensed milk.
Stirring continuously, let the mixture come to a boil.
Let it slow boil for 1 minute while stirring.
Take off the heat, and stir in the coconut.
As soon as the cake comes out of the oven, pour the topping on and spread over cake.