Preheat the oven to 350ºF (175ºC) and position an oven rack to the center position.

Grease an 8x8-inch baking pan well with butter.

In a medium bowl, whisk together the sweet rice flour, ginger, cinnamon, cardamom, cayenne, salt, and baking powder. Set aside.

Make Persimmon Purée: You’ll need ½ cup (140g) of persimmon purée for this recipe. Remove the calyx from the persimmon and then rip open the persimmon. Scoop out the persimmon flesh. Blend the persimmons in a food processor or use an immersion blender to blend. Measure out ½ cup of persimmon purée.

In a large bowl, whisk together the eggs, persimmon purée, coconut milk, butter, and the brown and white sugars. Add the molasses and vanilla extract and whisk until smooth.

Add the flour mixture to the wet ingredients all at once. Use a wooden spoon to mix everything together until well combined.

Pour the batter into the greased baking pan. Use an offset spatula or a rubber/silicone spatula to spread the batter to an even layer.

Bake the mochi for 60 to 65 minutes, rotating the pan after 30 minutes of baking. Let the mochi cool in the pan for 15 to 20 minutes before unmolding.

To unmold the mochi, flip the entire pan onto a wire cooling rack. Once the mochi drops from the pan, place another wire rack over the bottom of the mochi. Flip everything over once again so that the mochi is right-side up. Let the mochi cool completely before serving.

Slice the mochi into 16 or 20 pieces. Sprinkle powdered sugar on top of the mochi and serve.