Fluffy white cupcakes are the perfect springboard for the tropical flavor of mango. Cooking the mango puree intensifies its flavor, making it the perfect cupcake filling and flavoring for mango buttercream. I love the look of sliced almonds to finish these cupcakes but feel free to substitute chopped macadamia nuts or toasted coconut for a more tropical vibe.
For the cupcakes: Set a rack in the center of the oven and preheat to 350 degrees F. Line a 12-cup standard-size cupcake pan with 12 paper liners.
Place the butter, sugar, baking powder and salt in the bowl of a stand mixer fitted with the paddle attachment and mix on medium speed until uniformly sandy and no butter chunks remain, about 1 minute. Add the oil and vanilla and mix on high speed until very fluffy and almost white, 2 to 3 minutes.
With the mixer on low, add the egg and mix on medium speed for 30 seconds. Scrape down the paddle and the sides of the bowl. Add the egg white on low speed then increase to medium speed and mix until smooth and thick like whipped cream, 30 seconds to 1 minute. Alternate between adding flour and buttermilk in 3 additions of flour, mixing until the flour is incorporated. Scrape the bowl as needed between additions of flour and buttermilk.
Give the batter a few final folds with the spatula and divide among the 12 cups in the cupcake pan. Give the pan a few taps on the counter and bake in the center rack of the oven until a toothpick inserted in the center comes out with a few moist crumbs, 20 to 22 minutes. Cool the cupcakes in the pan for 5 minutes then remove and place on a wire rack to cool completely, about 1 hour.
For the mango purée: Place the mango purée, lime juice and sugar in a medium saucepan or skillet over medium heat and simmer, stirring for about 1 minute. Mix the cornstarch and water into a slurry in a small bowl and add to the saucepan. Simmer for about 1 more minute. The mixture will thicken and form large bubbles as it simmers. Transfer the purée to a clean, large rimmed plate and let cool completely, about 1 hour. You will have about 1 cup of thick mango puree.
Reserve 2/3 cup of the puree to be used in the buttercream and place the remaining puree into a
pastry bag or resealable plastic bag to fill the cupcakes.
For the buttercream: Beat the butter in a stand mixer fitted with the paddle attachment on medium-high speed until very smooth and shiny. Beat in half the mango puree, salt and vanilla on low speed, raising to medium speed once combined. Beat in the remaining puree and mix on high until smooth (the mixture will look like vanilla pudding). Add the confectioners’ sugar all at once and mix on low speed until combined. Stop and scrape the bowl and paddle and then mix on high speed until smooth and thick, 2 to 3 minutes, scraping the bowl and paddle as needed.
To assemble the cupcakes: Use a paring knife or apple corer to remove a 1-inch plug out of the center of each cupcake, going about halfway down. Reserve the cake cores. Use the mango puree in the pastry bag or resealable bag (snip off a corner) to fill each cupcake center with a heaping teaspoon of purée (there will be some leftover and that’s okay). Gently press the reserved cake cores back into place.
Place the buttercream into a pastry bag fitted with a star tip, if desired, or cut a 1/2-inch opening at the base of the bag and frost the cupcakes as desired. Gently press a handful of almond slices into the sides of the buttercream. Store the cupcakes covered and at room temperature for up to 2 days.