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  1. Preheat the oven to 350°F. Lightly grease the cups of a standard muffin pan; or line with papers, and grease the papers.

  2. To make the cake: Sift, then whisk together the first five ingredients; set aside.

  3. Whisk together the egg whites, milk, and flavors; set aside.

  4. Beat together the butter and sugar until the mixture is light and fluffy. Add the dry ingredients in three parts, alternating with the wet ingredients, mixing until combined.

  5. Scoop the into the prepared muffin cups.

  6. Bake for 16 to 20 minutes, until the cupcakes spring back when lightly touched in the center.

  7. Cool the cupcakes in the pan for 5 minutes then turn them out onto a rack to cool completely.

  8. To make the frosting: Pour the pineapple juice into a small saucepan and set over medium-high heat. Bring the juice to a boil, reduce the heat to medium, and allow the juice to simmer until reduced by 3/4; you want to end up with 3 tablespoons of juice.

  9. Transfer the juice to a heat-safe bowl and allow it to cool to room temperature.

  10. In a mixing bowl, beat together the butter, salt, meringue powder, and vanilla until fluffy.

  11. Add the sugar and juice, and beat well. Pipe or spread the frosting onto the cooled cupcakes.