MUNGGO FILLING: Soak Mung beans overnight. Drain and refresh water then bring to boil until the beans start to soften, reduce heat and cook until water is reduced just above the beans. Add the sugar and continue to cook until it starts to thicken. Transfer to a blender or use a stab mixer and pulse until it becomes smooth and fine. Put back to heat and add the flour and cook while stirring constantly until it turns into a thick paste. Remove from heat and let it cool down before using.
Alternatively, canned red beans can also be used and here is the recipe.
FOR THE FLAKY PASTRY Combine all ingredients for Dough 1 in a big bowl. Mix the ingredients using a fork or spoon until shortening or lard are cut into small pieces and covered with flour. Add more water if too dry. Knead just a couple of times until they stick together and then form into a ball and cover with plastic wrap or kitchen towel and set aside.
In a separate bowl, combine the ingredients for Dough 2. Mix well using your hands until a smooth dough is formed.
Roll Dough 1 into a rectangle about a half inch thick. Next place Dough 2 in between two sheets of plastic wrap or parchment paper and roll into a rectangle about 2/3 the size of Dough 1. Place Dough 2 on top of Dough 1 covering two-thirds of the rectangle from the left side. Fold the third uncovered part (from the right) over the center part. Then fold the remaining third part (from left) over both layers, making 3 layers in total. (like foldiging a letter).
Turn and roll the back to its original size and then repeat the three-fold process. Then do this again for the third time. After the last fold, let the dough rest for 5-10 minutes so the gluetn can relax and won't shrink back when rolled.
Roll the dough again into its original size(rectangle). Cut the dough into 2, lengthwise, then tightly roll each dough into 2 cylinders (like a jelly roll). Cut each cylinder into 12 equal parts. Place them in a bowl and cover with a wet paper towel or plastic wrap to avoid from getting dry.
Take a piece of dough and flatten with a rolling pin as thin as possible and try to make it round. Scoop a spoonful of the filling and place it in the middle. Gather the sides of the dough over the filling and pinch together to close. Take a round cookie cutter and insert the filled dough inside the circle, then with pinched side down press it against the counter to take form.
Place the Hopia on a baking sheet lined with parchment paper with the pinched side facing up and bake at 180°C/350°F for 15-20 minutes or until slightly golden, they will form a bulge while baking but that is ok. Take them out of the oven and now turn them so that the pinched side is now facing down and slightly press them flat using a spatula or slotted turner. Brush with egg wash and return them to the oven and bake for 5-10 minutes or until lightly browned.
Remove from oven and let them cool on a cooling rack.