In a large bowl, cream the softened butter, granulated sugar, and brown sugar together for 2–3 minutes until pale and fluffy. Proper creaming is key for a soft cookie.

Add the egg and mix until fully incorporated, scraping down the bowl. Mix in the mango purée and vanilla extract until smooth and evenly colored.

In a separate bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt.

Add the dry ingredients to the wet mixture and fold gently just until no dry pockets remain. Do not overmix; the dough should be soft and slightly tacky.

Chill the dough for 20 minutes. This prevents spreading and helps keep the cookies thick.

Scoop the dough into 45 g portions and roll lightly into balls. Place them on the prepared trays, leaving space between each.

Bake for 11–13 minutes, until the edges are set and the centers look just cooked but still soft. The tops should remain pale with minimal browning.

Let the cookies cool on the tray for 5 minutes, then transfer to a rack to cool completely before frosting.

To make the frosting, beat the softened butter for 2 minutes until creamy and smooth.

Add the powdered sugar in two additions, mixing well and scraping down the bowl.

Beat in the mango purée, vanilla extract, and salt. Continue whipping for 2–3 minutes until light and airy. If the frosting feels too thick to pipe, add milk a teaspoon at a time.

Transfer the frosting to a piping bag fitted with a star tip. Pipe a tight swirl onto each fully cooled cookie, starting from the center and working outward.

Allow the frosting to set for 15 minutes before serving, or refrigerate briefly for sharper swirls.