In small bowl, whisk together flour, baking powder, and salt; set aside. In separate small bowl, whisk together egg whites, cream of coconut, coconut milk and vanilla until well combined; set aside. In large bowl, using electric mixer on medium speed, beat together butter and sugar, occasionally scraping down sides of bowl with spatula, until light and fluffy, about 4 minutes. With mixer on low speed, alternately beat in reserved flour mixture and reserved coconut mixture in thirds, beginning and ending with flour mixture, beating until just blended. Then, continue to beat until smooth, about 1 minute.