First, soak the mung beans overnight or for a few hours to soften them faster. Cook or steam the mung beans until soft, then blend them with the durian and a little water in a blender until smooth. Transfer to a nonstick pan. In a bowl, mix the flour with the oil until the mixture flows like a ribbon when lifted. Add the remaining oil gradually while cooking the filling.

Start cooking the mixture over medium heat, stirring constantly to prevent burning. When it thickens slightly, add the flour mixture, then gradually add the rest of the oil. Continue stirring until the filling is smooth, dry, and no longer sticks to the pan (this part gets heavy to stir). Remove from heat. Mix in the cooked glutinous rice flour, return to the heat briefly to cook through, and add a little vanilla if you like.

Depending on your mold size, weigh the dough and filling. The ratio is 2:3 or 1:2. For a 5.3 oz (150 g) mold, use 3.2 oz (90 g) filling (including salted egg yolk) and 2.1 oz (60 g) dough. Weigh the filling, wrap it around the egg yolk, and roll into a ball.

Sift the flour into a bowl, make a well in the center, and add the other dough ingredients. Mix until smooth and elastic, but don't overmix or the dough will become tough. Cover with plastic wrap and let rest for 30 minutes. Then weigh and roll the dough into balls.

Flatten the dough, wrap it around the filling, and shape into balls. Preheat the oven to 350°F (180°C) with both top and bottom heat. Dust the mold with flour to prevent sticking, tap out the excess, press the dough ball into the mold, then place the shaped mooncake onto a baking tray lined with parchment paper.

Bake the mooncakes for 10 minutes. While baking, mix all the egg wash ingredients together.

When the mooncakes turn opaque white, remove from the oven and lightly mist with water. Let cool slightly, then brush with the egg wash.

Return to the oven at 350°F (180°C) for another 10 minutes. Since oven temperatures can vary, rotate the tray as needed and watch until the mooncakes are evenly golden brown. Remove from the oven and cool on a rack. The crust will be a bit firm at first, but after 1–2 days, the color deepens and the cakes become softer and more moist.