Beat the softened butter and granulated sugar in a large bowl with an electric mixer on medium speed until fluffy, about 3 minutes. Add the egg, ube halaya, ube extract, and vanilla extract. Beat until smooth and a deep purple color, about 1 to 2 minutes.
In a separate bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt.
Add the dry ingredients to the wet mixture and stir with a spatula until just combined. Fold in the white chocolate chips. Cover the dough and refrigerate for at least 1 hour until firm.
Preheat your oven to 350°F (177°C) and line baking sheets with parchment paper. Place the powdered sugar in a shallow bowl.
Scoop tablespoon-sized portions of dough and roll each into a smooth ball. Roll each ball in the powdered sugar until thickly coated. Place on the prepared baking sheets 2 inches apart.
Bake for 11 to 13 minutes until the cookies are puffed, crackled, and the edges are just set. The centers should look slightly soft.
Cool on the baking sheet for 10 minutes before transferring to a wire rack. The cookies will be soft, chewy, and stunningly purple with beautiful white crinkle cracks.