Rinse the mung beans until the water runs clear.

Add water to the mung beans and soak for at least 4 hours, preferably overnight.

Rinse the beans under running water and drain well. Transfer the soaked beans to a nonstick saucepan. Add just enough water to cover.

Set the saucepan over medium heat and bring the beans to a boil. As soon as it begins to bubble, cover and reduce the heat to very low.

Add the sugar, honey, salt, and butter.

Return the saucepan to medium-low heat and stir until the butter melts and the sugar and honey dissolve. As the butter melts, the paste will loosen.

As the moisture evaporates, the paste thickens and pulls away from the bottom of the pan. Continue stirring until the paste follows the motion of the spatula but still clings to it slightly.

Reduce the heat to the lowest setting to prevent the paste from burning. Continue cooking, stirring, until the paste is thick enough that it no longer sticks to the spatula. At this stage, the paste resembles modeling clay.

Transfer the paste to a bowl and divide it into two portions. Add matcha powder to one portion to color it. Mix well, pressing the paste with a spatula.

Let both portions cool until lukewarm. Cover the surface of the paste to prevent a skin from forming.

When the paste is lukewarm, divide each portion into five equal parts, about 50 g each. Roll each portion between your hands to form a ball. Cover the balls with plastic wrap to keep them from drying out.

Shape the mooncakes with a mooncake mold. Roll each ball of paste into an elongated cylinder with the palms of your hands. Gently place the paste into the mold and set the mold on a flat surface.

Gently press the handle to imprint the design. Press until it stops, then lift the handle to release the mooncake.

Repeat with the remaining balls of paste. It's important to mold the mooncakes while the paste is still warm but not hot.