Soak the mung beans overnight or at least 8 hours to soften. I use the same pot that I will boil it in the next day.
Drain and rinse the mung beans. Add water and bring mung beans to a boil. Boil until the water is reduced to the surface of the mung beans.
Turn off heat. Using a hand blender, blend the mung bean mixture until it is smooth.
In a separate container, mix the AP flour with enough water to make a thick paste or slurry. Add this slurry to your mung bean mixture and return it to medium heat, mixing continuously until it thickens the paste and the flour cooks off. It will thicken further as it cools.
Remove from heat. Put plastic wrap directly on the surface of the mixture so a skin does not form. Let it cool to room temperature.
Mix together the flour, vegetable shortening, and salt. Mix well until the shortening pieces are coated in flour. Optional: use a dough cutter to mix in the shortening.
Add the sugar water to the flour mixture and mix with fork until you have a shaggy dough.
Knead the mixture a few times just until it comes together. Flatten it into a disc and square off the edges so that it is easier to roll the dough later.
Combine all ingredients and mix with your hands. No need to be gentle here. Once it is well mixed, flatten it into a disc and square off the edges.
Combining the doughs
Let both doughs rest for at least 20 minutes
Roll dough #1 into a rectangle 1/4 inch thick.
Roll dough #2 into a rectangle that is 2/3 the size of Dough #1 rectangle
Place Dough #2 on top of Dough #1 along the edge so that 1/3 of dough #1 is exposed at the top
Fold the exposed dough #1 over the middle. Fold the remaining third over both layers, like folding a piece of paper in 3.
Turn the dough and roll it to the original size of dough #1. Repeat the 3 fold process. Turn the dough and repeat for a third time.
Let the dough rest for 20 minutes.
Scoop the mung bean paste into 24 equal scoops and cover loosely
Roll the dough out into a large rectangle.
Cut the dough in half, lengthwise
Tightly roll one half of the dough like a cinnamon roll or jelly roll, leaving the seam side down. Repeat with the other half
Cut each roll into 12 equal pieces. Cover with plastic wrap
Rolling out one piece of dough at a time, leave the seam side down and flatten the dough as thin as possible (You want it large enough to be able to cover and seal the mung bean mixture in the center).
Fill the center of the dough with the mung bean mixture and wrap the dough, pinching it at the top to seal.
Insert the filled pastry into a round cutter, about 2" in diameter.
Press down on the pastry to form the hopia into a perfect circle.
Repeat the assembly steps until you have made all 24 hopia. After assembling 12 hopia, preheat the oven to 350*.
Place all 24 hopia on one parchment lined half sheet with the pinched side facing up. Bake for 20-22 minutes on the middle rack, or until slightly golden. Be sure that the hopia are golden or lightly browned before proceeding to the next step or they will lose their flat top.
Mix together your egg with water to make the egg wash.
Remove the sheet from the oven and turn the hopia so that the pinched side is facing down.
Press down slightly on the hopia with a flat spatula. Brush the tops with your egg wash
Return to the oven and bake for another 8-10 minutes, or until golden brown on top.
Let hopia cool completely before serving.
Yellow mung beans are critical! I made the mistake of buying green mung beans that I use for another Filipino recipe, munggo, and I learned the hard way that you have to shell each green mung bean. You can find yellow mung beans as moong dal, split mung beans, yellow mung bean dal. Resting allows the gluten to relax so your dough doesn't shrink too much during baking. It also makes your dough easier to handle. You can skip the 2" cookie cutter and go for a more rustic look. For a more polished look, gather the folds in the same direction when wrapping the dough around the filling. This will give it a spiral look on the side. By learning this folding technique, you're preparing yourself to make flaky hand pies or egg tarts!