2 Cups water
1 Tbsp Hibiscus Powder
1/2 Cup sugar
1 tsp finely Coarse Ground Lemon Peel
1 tsp finely Coarse Ground Lime Peel
1 tsp finely Coarse Ground Orange Peel
1-3/4 Cups cake flour
1-1/2 tsp baking powder
1/2 tsp Salt
2/3 Cup buttermilk
4 large egg whites
1/4 tsp coconut extract
1-1/3 Cups sugar
10 Tbsp (1-1/4 sticks) unsalted butter, room temperature
1-1/2 Cups chilled heavy whipping cream
4 Tbsp sweetened cream of coconut (such as Coco López), divided
1 Cup sweetened flaked coconut, lightly toasted
In a small saucepan, bring 2 Cups water to boil on the stove. Add hibiscus powder and sugar to the water and bring mixture to a boil, stirring steadily until sugar dissolves. Boil gently over medium heat until sugar-liquid is reduced to 1 Cup, about 10-12 min. Remove pan from heat. Stir in lemon peel, lime peel, and orange peel; allow to steep 10 min.
Using a fine sieve, strain sauce into bowl. Cover the bowl and chill until cold, at least 2 hours. [DO AHEAD: The hibiscus-fruity-syrup can be made up to 3 days ahead. Keep chilled until ready to use.]
Preheat oven to 350°F and butter a 13 x 9 x 2-inch metal baking pan. Combine dry ingredients (flour, baking powder, and salt) in medium bowl. In another medium bowl, whisk liquid ingredients (buttermilk, egg whites, and coconut extract).
Using electric mixer on low speed, beat sugar and butter in large mixing bowl until light and fluffy. Add dry (flour) mixture to butter mixture in 3 “batches” alternately with the liquid (buttermilk) mixture in 2 “batches,” making sure to blend the mixture well between additions, and periodically scraping bottom and sides of bowl with a rubber spatula. Transfer batter to prepared baking pan; spread evenly.
Bake cake in 350°F oven until it appears pale golden on top, and a tester inserted into the center comes out mostly clean, but with some crumbs attached, 29 to 32 min. Remove cake from oven and allow to cool completely in the baking pan on a cooling rack. [DO AHEAD: The cake can be baked up to 1 day ahead. Once it has cooled, cover the pan tightly and store cake at room temperature.]
Using an electric mixer and whisk attachment, whip the cream and 2 Tbsp cream of coconut in large bowl until peaks form. Spread the whipped topping over the top of cake. Drizzle 2 additional Tbsp cream of coconut over the whipped cream, and, using a dinner knife, swirl the cream of coconut throughout whipped cream. Sprinkle toasted coconut over the surface of the cake.
Cut the cake into squares; transfer to dessert plates. Drizzle hibiscus sauce around cake.