Piña Colada Cake | America's Test Kitchen

Ingredients

• 2 cups (8 ounces/227 grams) cake flour
• 1½ cups (10½ ounces/298 grams) granulated sugar , divided
• 1 teaspoon baking powder
• ¼ teaspoon baking soda
• ¾ teaspoon salt
• ¾ cup buttermilk
• 5 large egg yolks plus 3 large egg whites, divided
• 8 tablespoons unsalted butter , melted and cooled
• 3 tablespoons vegetable oil
• 1½ teaspoons vanilla extract
• ⅛ teaspoon cream of tartar
• 1 tablespoon instant tapioca
• 1 pineapple , peeled, cored, and quartered lengthwise
• ⅓ cup (2⅓ ounces/66 grams) granulated sugar
• ¼ cup spiced rum
• ¼ teaspoon table salt , divided
• 20 tablespoons 2½ sticks) unsalted butter , softened, divided
• 3 tablespoons canned coconut milk
• 1 teaspoon vanilla extract
• ½ teaspoon coconut extract
• 2¼ cups (9 ounces/255 grams) confectioners' sugar
• 1 cup (3 ounces/85 grams) shredded coconut , toasted