Coconut Sheet Cake with Hibiscus Sauce

Name: Coconut Sheet Cake with Hibiscus Sauce
Ingredients: 2 cups water; 1 cup dried hibiscus flowers (about 1 1/2 ounces); 1/2 cup sugar; 1 teaspoon finely grated lemon peel; 1 teaspoon finely grated lime peel; 1 teaspoon finely grated orange peel; 1 3/4 cups cake flour; 1 1/2 teaspoons baking powder; 1/2 teaspoon salt; 2/3 cup buttermilk; 4 large egg whites; 1/4 teaspoon coconut extract; 1 1/3 cups sugar; 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; Ingredient info: Dried hibiscus flowers, also called jamaica flowers, are available at some natural foods stores and at Latin markets. Look for sweetened cream of coconut in the liquor section of most supermarkets.; Test-kitchen tip: When you're reducing the hibiscus sauce, spoon a bit of the hot sauce on a chilled plate to see how thick it will be when it is refrigerated.