Preheat the oven to 325 degrees and spray a 9x13 inch baking pan with nonstick cooking spray.
In the bowl of an electric mixer, add cake mix, fruit cocktail with syrup, 1 cup of the coconut and the eggs. Mix on medium low for 2 minutes, or until well blended. Pour into prepared pan. Sprinkle with brown sugar. Bake 45 minutes, or until set but don't overbake.
While cake is cooking, make topping by heating the butter, sugar and milk on medium low in a saucepan, stirring occasionally. Once it boils, boil for 2 minutes. Remove from heat and add remaining coconut. Pour over hot cake when removed from oven. Serve warm or cool.