Preheat oven to 350.
Grease and flour 9x13in baking pan.
Melt ⅔ cup butter.
Blend cake mix, 4 eggs, ½ cup sour cream, and 1 cup milk. Beat with a mixer for 30 seconds, slowly adding in melted butter. Then on medium speed for 2 minutes.
Bake 23-28 minutes.
Immediately poke holes with fork.
Shake cream of coconut really good, then open can.
Pour and spread coconut cream over the entire sheet cake.
Cover and refrigerate 1 hour to completely cool.
Meanwhile make frosting.
In a stand mixer, whip 2 sticks of softened butter on medium-high speed until very fluffy (about 5 minutes).
Add in 3 cups of powdered sugar a little at a time beating on low speed to incorporate.
Add in 1 tsp of vanilla, 2 tbs milk, and a pinch of salt. Mix until completely on low speed until completely incorporated.
Adjust mixer to medium high speed. Beat until frosting is light, fluffly, and spreadable with no lumps.
Spread frosting evenly on cold cake.
Evenly top frosting with 8 oz shredded coconut.