Preheat oven to 350°. Beat butter and sugar at medium speed with a heavy-duty electric stand mixer, using paddle attachment, until fluffy. Add egg yolks, 1 1/2 cups cream of coconut, and 1 1/2 tsp. vanilla, beating until blended.
Whisk together flour and next 3 ingredients; add to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed until blended after each addition, stopping to scrape down bowl as needed. Transfer to a very large bowl.
Beat egg whites, using whisk attachment, at high speed until stiff peaks form (about 2 minutes). Stir one-fourth beaten egg whites into batter; fold in remaining egg whites.
Divide cake batter among 3 greased and floured 9-inch round cake pans with 2-inch sides. Bake at 350° for 35 to 40 minutes or until a wooden pick inserted in the center comes out clean. Cool in pans on wire racks for 10 minutes; remove from pans and continue to cool on wire racks completely (about 1 hour).
Beat heavy cream, dash of salt, remaining 1/2 cup cream of coconut, and remaining 1/2 tsp. vanilla at medium speed with an electric mixer until stiff peaks form (about 3 minutes).
Place 1 cake layer on a serving plate or cake stand; spread with 1 1/4 cups whipped cream mixture, and sprinkle with 3/4 cup coconut. Top with second cake layer; spread with 1 1/4 cups whipped cream mixture, and sprinkle with 3/4 cup coconut. Top with remaining cake layer. Spread remaining whipped cream mixture over top and sides of cake. Gently press remaining coconut into whipped cream mixture on top and sides of cake. Cover and chill 4 to 24 hours. Store cake in refrigerator. Let stand at room temperature 1 hour before serving.
This recipe is excerpted with permission from <a href="http://www.amazon.com/gp/product/0848739663/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0848739663&linkCode=as2&tag=craftfocom-20">"Christmas with Southern Living 2013: The Ultimate Guide to Holiday Cooking & Decorating"</a> by the Editors of Southern Living Magazine and published by Oxmoor House.