Rinse the split mung beans under cool running water to remove any dirt or grit. Optionally, you may soak them in 3 cups water for 8 hours, but due to their small size, soaking mung beans isn't necessary. 1 cup dried split beans will yield 3 cups after soaking.
Whether soaked or unsoaked, add the mung beans to the Instant Pot with 1 1/2 cups water. Cover and seal the lid and pressure cook using the Beans setting. Allow for a Natural Pressure release.
Using a rubber spatula, stir and smash the cooked beans, then add salt, oil and butter. Turn on the Saute setting and use the rubber spatula to stir ingredients together until a smooth paste forms and oil is absorbed. Stir in the sugar and continue cooking for an additional 5 minutes.
If adding color, divide the dough into equal sized portions. Mix thoroughly to the desired color preferred. I used about 5 grams dry food powder color for each portion.
Optionally, for a smoother consistency, use a silicone spatula to press each batch of dough, one at a time, through a fine mesh sieve. Scrape any remaining dough on the underside of the sieve into a bowl.
Using a food scoop or kitchen scale, portion dough into balls weighing 50 grams (scant 4 tablespoons) each. Press each dough ball into a moon cake mold (See Note 3) using any design you prefer. Place each dessert on tray lined with silpat or square of parchment paper (See Note 4).
Serve immediately at room temperature. If storing, the cakes will keep 1 week covered in the refrigerator.