In a medium saucepan over medium heat, cook 200g of frozen mangoes until they soften, about 5-7 minutes. Mash and stir in 1 tablespoon of white sugar until combined, form a jam consistency and refrigerate.

Soak 0.25 cup of sweet rice in boiling water for about 20 minutes. Drain and steam in a bamboo steamer for about 15 minutes. Combine with 0.33 cup of coconut milk and 3 tablespoons of sweetened condensed milk. Reserve 1 tablespoon for the cookie dough.

In a mixing bowl, cream together 113g of softened unsalted butter, 100g of light brown sugar, and 50g of white sugar until fluffy (3-5 minutes). Blend in 1 egg yolk, the thick part of 1 egg white, 0.5 teaspoon of vanilla extract, and 1 tablespoon of reserved coconut cream until well incorporated.

In a separate bowl, whisk together 0.5 teaspoon of baking soda, 0.25 teaspoon of salt, and 180g of all-purpose flour. Gradually mix into wet ingredients until just combined.

Cover the cookie dough and chill in the refrigerator for at least 30 minutes. Preheat your oven to 350°F (175°C) and prepare a baking tray lined with parchment paper.

Scoop out chilled dough portions, flatten them, and swirl in pieces of the sticky rice mixture and a dollop of mango jam into each cookie. Bake for 13-15 minutes or until edges are golden brown.

Let cookies cool on tray for 10 minutes before transferring to a wire rack. Enjoy warm or store in an airtight container.