- 1 cup dried hibiscus flowers (about 1 1/2 ounces)
- 1 teaspoon finely grated lemon peel
- 1 teaspoon finely grated lime peel
- 1 teaspoon teaspoon finely grated orange peel
- 1 1/2 teaspoons baking powder
- 1/4 teaspoon coconut extract
- 10 tablespoons (1 1/4 sticks) unsalted butter, room temperature
- 1 1/2 cups chilled heavy whipping cream
- 4 tablespoons sweetened cream of coconut (such as Coco López), divided
- 1 cup sweetened flaked coconut, lightly toasted
Bring 2 cups water to boil in small saucepan. Stir in hibiscus flowers. Remove from heat; let steep uncovered 10 minutes.
Pour hibiscus mixture through fine-mesh sieve set over bowl, pressing on solids to extract all liquid; discard solids. Return hibiscus liquid to same saucepan. Add sugar; bring to boil, stirring until sugar dissolves. Boil gently over medium heat until liquid is reduced to 1 cup, 10 to 12 minutes. Remove from heat. Stir in lemon peel, lime peel, and orange peel; steep 10 minutes. Strain sauce into bowl. Cover; chill until cold, at least 2 hours. DO AHEAD Can be made 3 days ahead. Keep chilled.
Preheat oven to 350°F. Butter 13x9x2-inch metal baking pan. Whisk flour, baking powder, and salt in medium bowl. Whisk buttermilk, egg whites, and coconut extract in another medium bowl. Using electric mixer, beat sugar and butter in large bowl until light and fluffy. Add flour mixture to butter mixture in 3 additions alternately with buttermilk mixture in 2 additions, beating to blend well between additions and occasionally scraping bottom and sides of bowl with rubber spatula. Transfer batter to pan; spread evenly.
Bake cake until pale golden and tester inserted into center comes out with some crumbs attached, 29 to 32 minutes. Cool cake completely in pan on rack. DO AHEAD Can be made 1 day ahead. Cover pan tightly and store cake at room temperature.
Using electric mixer, beat whipping cream and 2 tablespoons cream of coconut in large bowl until peaks form. Spread whipped cream over top of cake. Drizzle 2 tablespoons cream of coconut over whipped cream. Using table knife, swirl cream of coconut throughout whipped cream. Sprinkle toasted coconut over.
Cut cake into squares; transfer to plates. Drizzle hibiscus sauce around cake.