1-Cream butter and sugar: Cream butter and sugar. Place the butter, sugar, and vanilla extract into a large mixing bowl. With a handheld mixer or a stand mixer fitted with the paddle attachment, beat on high speed until creamy, for 2 to 3 minutes.
2-Add liquid ingredients: Add liquid ingredients. Add the egg and pour in the milk. Mix on low speed until incorporated. Occasionally, scrape down the sides and bottom of the bowl.
3-Stir in dry ingredients: Stir in dry ingredients. With the mixer running on low, stir in the flour and baking powder. Mix until everything is just combined, and you no longer see streaks of flour. Be careful not to overmix. The batter will appear creamy, thick, and sticky.
4-Fold in mango: Fold in mango. With a spatula or large spoon, gently fold the mango chunks into the cookie dough. Work carefully so the fruit pieces remain intact and don’t squish.
5-Chill cookie dough: Chill cookie dough. Cover the mixing bowl tightly with plastic wrap and chill the dough in the fridge for 30 minutes to an hour (and up to 2 days).
6-Prepare for baking: Prepare for baking. Adjust a baking rack in the center of the oven and preheat the oven to 350°F / 180°C / gas mark 4. Line 2 baking sheets with parchment paper. Set aside.
7-Shape cookies: Shape cookies. Take the dough out of the fridge. Scoop portions of dough, 1.5 tablespoons each, and place them 3 in / 9 cm apart on the prepared baking sheets.
8-Bake: Bake. Bake the mango cookies for 14 to 16 minutes or until a cookie springs back when gently poked with your finger.
9-Cool: Cool. Remove the cookies from the oven and let cool on the baking sheet (tray) for 10 minutes. Then transfer them onto a wire rack to cool completely.
10-Make glaze: Make glaze. In a small mixing bowl, whisk the powdered sugar, vanilla extract, and milk (or mango juice if using) until smooth. If needed, add more powdered sugar to thicken the glaze, or more milk to thin it out.
11-Decorate mango cookies: Decorate mango cookies. Drizzle the glaze over the cookies and let set.