Preheat the oven to 350F/180 degree celcius. Line an 8 by 8-inch baking pan with parchment paper.
In a medium bowl, add mochiko, cocoa powder, sugar and baking powder. Whisk together until evenly mixed.
In a large bowl, add melted butter, eggs, milk, and vanilla extract. Whisk until evenly combined and no egg streaks remain. Add in dry ingredients. Mix until evenly blended.
Pour batter into prepared baking pan. Sprinkle surface with chopped chocolate.
Bake 60-70 minutes or until mochi is set. A toothpick inserted should come out mostly clean. Let mochi cool completely before slicing and serving.
