Soak mung beans overnight or at least 1 hr in warm water. Steam until soften and easily smashed with your finger tips, roughly 20 minutes (or longer if not soaked overnight). In meantime, dissolve sugar in warm water. When mung bean has cooled, transfer to mixing bowl and coarsely mash. Add the sugar water mixture and coconut and mix well. The texture should be like mashed potatoes. Allow to cool and form small quarter size balls of mung bean. Refrigerate covered.
Add sugar in 2 1/2 cup of warm water and stir to dissolve. In large mixing bowl, add sugar mixture and the potato flakes and stir to combine. Then add the baking powder and stir to dissolve. Finally add the two types of rice flour and mix together to form a big ball of dough. There is no need to knead the dough. The dough should be a wet play-dough consistency. Add a few tablespoons at a time of the extra 1/4 cup of water to the dough and mix well if it's too dry or gets to dry when working.
Pinch off a golf ball sized piece of dough and form into a ball. Flatten to a disk with palm of your hands and thin out the edges to form a pancake. If the dough cracks at the edges, it's too dry. Add a few tablespoons at a time of the 1/4 cup of water to the dough and mix well. Place the filling in the center and fold dough edges together and seal seams by rolling in the palm your hands.
Roll in a bowl of sesame seeds to cover completely. Roll in the palm of your hands to make sure the sesame seeds stick. Cover loosely at room temperature until ready to fry.
In a small dutch oven filled about 1/3rd way with oil, heat to 325 degrees. Add multiple banh cam to nearly cover the pot and occasionally turn the banh cam for even frying. When golden brown, remove and drain and enjoy while warm.
Filling can be made 1-2 days in advance and kept refrigerated. To reheat, toast in toaster oven until crispy.