Preheat the oven to 350 degrees F. Lightly coat a 12X18-inch rimmed baking sheet with nonstick cooking spray. Set aside.
In a large bowl combine the flour, sugar, salt and baking powder; set aside. In a medium saucepan combine the butter and water and bring to a boil. Once it comes to a rolling boil, remove from the heat and stir it into the flour mixture until combined. Whisk in the sour cream, eggs, almond extract and coconut (if using).
Spread the batter evenly into the prepared pan and bake for 20-25 minutes.
Toward the end of the baking time for the cake, in a saucepan, combine the butter and milk for the icing. Bring to a boil over medium heat, stirring occasionally. Remove from the heat and whisk in the almond extract and then gradually whisk in the powdered sugar until smooth.
Once the cake has been taken out of the oven, pour the icing over the warm cake.
Notes
Halving the Recipe: ok, let's talk. You could {probably} halve the recipe for a 9X13-inch pan but I haven't tried it yet so experiment and let me know how it goes. Coconut Version: also, if you just want to take this to a coconut-crazy level (which I've done and absolutely died over), sub the butter for organic, extra-virgin coconut oil in the cake and the icing, switch out the almond extract for coconut extract (or vanilla extract) and sprinkle toasted coconut over the top of the iced cake. Coconut Oil:the coconut oil gives it a slightly sweeter taste but is delicious. I've made it the original way (as posted) and also the coconut way and both are phenomenal. Extract:if you don't love the flavor of almond extract, sub in vanilla extract.