Prepare the sticky rice by following my Rice Cooker Mango Sticky Rice recipe. Once finished, set aside enough sticky rice for topping the cookies and allow it to cool.
Add the diced mango, sugar, and lime juice to a small saucepan. Cook over medium-low heat for about 5 minutes, stirring occasionally, until the mango softens.
In a small bowl, whisk together the cornstarch and water until smooth. Stir the slurry into the mango mixture and continue cooking over low heat for 2–3 minutes, or until the puree is thick, glossy, and spreadable. Remove from the heat and let it cool completely.
In a large bowl, beat the softened butter and sugar until light and fluffy.
Mix in the egg yolk, 2 tablespoons of the cooled mango puree, and vanilla extract until smooth.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually fold the dry ingredients into the wet ingredients until no dry streaks remain. Do not overmix.
Cover and chill the dough for 15 minutes.
Preheat the oven to 350°F and line a baking sheet with parchment paper.
Using a cookie scoop, portion the dough onto the prepared baking sheet, leaving about 2 inches between each cookie.
Gently flatten each dough ball into a thick disc.
Top each cookie with a small spoonful of cooled sticky rice, then add a dollop of mango puree on top.
Bake for 14–16 minutes for smaller cookies (3 tbsp) or 17-20 minutes for larger cookies (mine was 4 tbsp scoops) or until the edges are lightly golden and the centers are just set.
Let the cookies cool on the baking sheet for 10 minutes before transferring them to a wire rack to cool completely.