Brown butter: Heat a small saucepan over medium heat. Add butter to the pan and stir frequently until it browns. Remove from heat and transfer to a container to cool.
Combine wet ingredients: Mash 1-2 ripe peaches to get 1 cup of mashed peaches. In a mixing bowl, add brown butter, mashed peaches, eggs, coconut milk, apple cider vinegar, vanilla extract, and miso. Mix until smooth.
Combine dry ingredients, make batter: In another bowl, whisk together rice flour, baking soda, baking powder, sugar, and salt. Slowly pour into wet ingredients, whisking to make a smooth batter.
Assemble and bake: Preheat oven to 350°F. Grease a 9x9 inch pan. Arrange peach slices in the pan. In a saucepan, mix brown sugar, whiskey, and miso. Pour over peaches. Add mochi batter. Bake for an hour. Let cool before flipping and serving.
