In a medium saucepan, heat 2 cups of frozen mangoes over medium heat for about 5–7 minutes, stirring occasionally until softened. Mash the mangoes with a fork and mix in ½ cup of white sugar until it reaches a jam-like consistency. Once done, transfer the mixture to a bowl and refrigerate to cool while you prepare the rest of the recipe.

Soak 1 cup of sweet rice in boiling water for 20 minutes to help it soften. After soaking, steam the rice in a bamboo steamer lined with cheesecloth or a heatproof plate for 15 minutes, or until slightly underdone. Once it’s done steaming, mix the rice with ½ cup of coconut milk and ¼ cup of sweetened condensed milk, ensuring it's well-coated, then reserve a tablespoon of this mixture for the cookie dough.

In a large mixing bowl, cream together ½ cup of softened unsalted butter, ¼ cup of light brown sugar, and ¼ cup of white sugar with a hand mixer until fluffy and pale; this should take about 3–4 minutes. Add in 1 egg yolk, 1 thick egg white, 1 teaspoon of vanilla extract, and the reserved tablespoon of coconut cream, mixing until fully incorporated.

In another bowl, whisk together 1 teaspoon of baking soda, a pinch of salt, and 1 ½ cups of all-purpose flour. Gradually blend the dry mixture into the wet dough until just combined to prevent overmixing, which keeps your Mango Sticky Rice Cookies chewy.

Cover the cookie dough tightly with plastic wrap or transfer it to an airtight container, and chill it in the refrigerator for at least 30 minutes. This resting period allows the flavors to meld and helps the cookies maintain their shape during baking, ensuring a perfect texture.

Preheat your oven to 350°F (175°C) and line a baking tray with parchment paper. Gently fold in the prepared mango jam and sticky rice into the chilled cookie dough until evenly distributed. Using a cookie scoop, portion out the dough onto the baking tray, optionally topping each ball with black sesame seeds or flaky sea salt for added flair.

Place the tray in the preheated oven and bake the cookies for 13–15 minutes, or until the edges are golden brown and the centers appear set. Remove the tray from the oven and allow the cookies to cool on the tray for about 10 minutes before transferring them to a wire rack to cool completely.