In a stand mixer with the paddle attachment, cream together the butter, brown sugar, and white granulated sugar on a medium-high speed. Cream until light and fluffy, about 5 minutes.
Add in the egg and mix on a low speed until just incorporated. Next, add in the ube halaya and the ube flavoring and mix to combine.
Sift the flour and baking powder into a separate bowl. While mixing on a low speed, gradually add in the sifted dry ingredients as well as the kosher salt. Mix until incorporated, do not over mix.
Remove the bowl from the stand mixer and cover it with plastic wrap. Place dough in the fridge to rest for at least 1 hour. (Dough can be made a day in advance if needed)
Preheat oven to 350°F. Place the powdered sugar in a bowl and line a baking sheet with a silpat or parchment paper. Use a 1 tbsp cookie scoop to portion the dough and form them into balls. Next, roll the dough in the powdered sugar to coat, and evenly space them on the baking sheet.
Bake in the preheated oven for about 13 minutes or until done.