Combine Japanese glutinous rice flour, white sugar, and baking powder in mixing bowl, whisk to aerate and combine.

In KitchenAid mixing bowl, add purple yam jam, egg, milk, coconut milk, miso, melted butter, vanilla extract, ube extract, purple color, then beat with paddle attachment on medium-low speed until well mixed about 2–3 minutes, then gradually add all dry ingredients, mix for 30 seconds more until combined, then transfer cake batter to cooler and allow to rest for 30 minutes.

Pour batter into buttered pans / molds, then bake for 60 minutes at 180°C, open oven door slightly and allow to rest in hot oven for 15 more minutes, then remove cake and cool for service.