In a bowl of a stand mixer with a paddle attachment, add in the softened butter and sugars. Beat butter mixture on medium-high speed until creamy and lightened in color.
Add in the egg, vanilla extract and use a spatula to scrape down the sides of the bowl.
Add in all-purpose flour, mochiko flour, baking soda, and baking powder and stir with the paddle on low speed to incorporate.
Fold in the chopped white rabbit candies and chocolate chips.
Use a small ice cream scoop (or tablespoon) and scoop cookie dough onto a cookie sheet or baking tray lined with parchment paper. (If baking on the same tray, be sure to leave a few inches of space for the cookie to spread).
Press additional chocolate chips and White Rabbit candies onto the cookie dough.
Chill in the fridge for 10-15 minutes.
Preheat oven to 350°F/177°C.
Bake the cookies, about 5 or 6 on a tray for about 8-10 minutes, or until golden brown.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire cooling rack. Sprinkle on flaked sea salt if desired.