For The Cake, Place A Rack In The Center Of The Oven, And Preheat The Oven To 350°F.
Lightly Grease And Flour A 13″ × 9″ Baking Pan And Set It Aside.
Place The Soft Butter And Sugar In A Large Mixing Bowl, And Blend With An Electric Mixer On Medium Speed Until The Mixture Is Creamy, 2 Minutes.
Add The Eggs, And Blend On Medium Until The Batter Is Smooth And Light, 2 Minutes More.
In A Separate Bowl, Stir Together The Flour, Baking Powder, And Salt.
Add To The Batter Along With The Buttermilk And Vanilla, Beginning And Ending With The Flour Mixture.
Blend On Low Until Everything Is Incorporated, Then Increase The Mixer Speed To Medium And Blend To Lighten The Batter, 30 Seconds More.
Turn The Batter Into The Prepared Pan, And Smooth The Top.
Place The Pan In The Oven.
Bake The Cake Until It Is Golden Brown And The Top Springs Back When Lightly Pressed, 28 To 32 Minutes.
Remove The Cake From The Oven.
Turn The Oven Broiler On, And Carefully Position A Broiler Rack 4″ To 5″ From The Broiler.
For The Topping, Place The Butter In A Medium-Size Saucepan Over Medium Heat To Melt, 1 Minute.
Stir In The Brown Sugar And Cream And Let The Mixture Come To A Boil And Boil For 2 Minutes, Or Until It Thickens Slightly.
Take The Pan Off The Heat.
Stir In The Coconut, Vanilla, And Salt.
Pour The Topping Over The Top Of The Warm Cake, Spreading It Out To Reach The Edges.
Place The Cake In The Oven, Leaving The Door Ajar Or The Oven Light On So You Can Watch The Broiling So It Will Not Overcook.
Let The Topping Broil Until It Bubbles Up And The Coconut Caramelizes, From 30 Seconds To 1 Minute, Depending On Your Broiler.
Remove The Pan From The Oven, Let It Rest For 15 Minutes, Then Cut Into Squares And Serve Warm.
