Weigh and sift all brown sugar, flour, baking powder, cocoa powder, salt and instant coffee into a medium bowl. Whisk to combine well, then set aside.
Preheat oven to 350°F or 180°C. Grease the muffin tray with melted butter and set aside.
Pour the remaining butter into a medium bowl or measuring jar along with milk and egg. Whisk to combine well.
Add in the dry ingredients and whisk again to combine.
Pour and divide mixture evenly into 12 muffin holes. Top each with chocolate chips.
Bake for 40 minutes or until top crust is fully formed but slightly springy to the touch.
Chill them on cooling rack for 10 minutes. Using a toothpick, push each out from the side.
Mochiko is a type of glutinous rice flour or sweet rice flour made from Japanese rice. You can find this product on Amazon or some local grocers. It can also be substituted with regular glutinous rice flour.