Make wrapper dough:

• Combine sweet rice flour, white rice flour, wheat starch, and sugar in a shallow, heat-proof bowl. Add soy milk and oil, and stir with a whisk until no lumps remain. Let rest for 30 minutes. Steam in a steamer over boiling water for 25-30 minutes (depending on the depth of the bowl), until dough becomes slightly translucent.*
• Remove from heat and stir vigorously, then invert onto an oiled surface or a piece of parchment paper, and knead (either folding with a spatula or with gloved hands) until smooth and elastic. Place in the refrigerator to harden for at least two hours.

To make filling:

• White bean matcha paste: drain the cooked beans and place in a food processor, blending until smooth. You may need to add 2 or 3 tablespoons of water in this step. Pour the purée into a medium saucepan, add the sugar and a pinch of salt, and cook over medium heat, stirring continuously until most of the water has been cooked away and the purée has thickened to a consistency similar to hummus.  Add coconut oil and matcha powder and stir well, continuing to cook over medium heat until the purée becomes glossy and forms a soft dough that sticks to the spoon in one mass, about 4 to 5 minutes. Remove from heat and chill until ready to use.
• Purple sweet potato paste: steam purple sweet potatoes until tender. I used my Instant Pot to cook them (set to 15 minutes on HIGH + natural pressure release). Peel and cut into small cubes, then place in a food processor with a few tablespoons of water, blending until smooth. Pour the sweet potato purée into a medium saucepan, add sugar and a pinch of salt, and cook over medium heat, stirring continuously until most of the water has been cooked away. Add coconut oil and stir well, continuing to cook over medium heat until the purée becomes glossy and forms a soft dough that sticks to the spoon in one mass, about 4 to 5 minutes. Remove from heat and chill until ready to use.
• White lotus seed paste: drain the cooked lotus seeds and place in a food processor, blending until smooth. You may need to add 2 or 3 tablespoons of water in this step. Pour the purée into a medium saucepan, add the sugar and a pinch of salt, and cook over medium heat, stirring continuously until most of the water has been cooked away and the purée has thickened to a consistency similar to hummus.  Add coconut oil and stir well, continuing to cook over medium heat until the purée becomes glossy and forms a soft dough that sticks to the spoon in one mass, about 4 to 5 minutes. Remove from heat and chill until ready to use.

Make dusting flour:

• In a medium pan, toast the sweet rice flour on medium-low heat until the flour turns light yellow. Remove from heat and set aside to cool.

To assemble mooncake:

• Divide the cold mochi dough into 12 equal pieces, 25g each. Shape the cooled filling into 12 balls of equal size, 25g each (you will have filling leftover).  I use a small kitchen scale to weigh each portion for consistency.
• Flatten a piece of dough onto a sheet of parchment paper, place another piece of parchment paper on top, and roll out gently into a round. Uncover and place a ball of filling in the center of the round, then gently wrap the dough upwards and around the filling, pinching edges at the top to seal. (Coat your fingertips liberally with the dusting flour to prevent sticking!)
• Dust the mooncake stamp (the mini mooncake size is for 50g) with flour, then shake to remove excess. Place the ball into the mooncake mould, stamp firmly, and push gently to remove. If you find the mooncake is sticking, you may need to dust the stamp with more flour, especially in the crevices.
• The mooncakes taste best after being chilled in the fridge. Store in an airtight container for up to 3 days, or freeze them for long-term storage (enjoy after thawing).