In a medium saucepan over medium heat, add your frozen mangoes and cook for about 5-7 minutes until softened. Using a fork or potato masher, mash the mangoes, then add white sugar and continue to cook for another 10 minutes until the mixture thickens into a jam-like consistency. Let it cool in the fridge while you continue with the recipe.

Start by soaking sweet rice in boiling water for 20 minutes to soften it. After soaking, drain the rice and place it in a steamer lined with a clean cloth; steam for approximately 25 minutes until the rice is slightly underdone but tender. Once cooked, combine the hot sticky rice with heated coconut milk and sweetened condensed milk, mixing until well-coated, and reserve one tablespoon for the dough.

In a large mixing bowl, cream together unsalted butter, light brown sugar, and white sugar until the mixture is light and fluffy, about 3-5 minutes. Then, add the egg yolk, thick egg white, vanilla extract, and the reserved tablespoon of coconut cream, mixing well. Gradually incorporate baking soda and salt, followed by the all-purpose flour, mixing until just combined to avoid overworking the dough.

Preheat your oven to 350°F (175°C) and line a baking tray with parchment paper. Take chilled cookie dough and dollop sticky rice and mango jam in the center; gently swirl the jam into the dough. Portion out the dough and any desired toppings like black sesame seeds or flaky sea salt. Bake for 13-15 minutes until edges are golden and centers appear slightly puffed, then cool on the tray for 10 minutes before transferring to a wire rack.

For an added burst of flavor, sprinkle flaky sea salt over the warm Mango Sticky Rice Cookies right after they come out of the oven.