Prep: Preheat oven to 350 F. Line two large baking sheet with parchment paper.
Make the dough: Using a hand mixer fitted with beaters or a stand mixer with a paddle attachment, cream butter, sugar and ube extract together until no lumps of butter remain.
226 grams unsalted butter, 200 grams granulated sugar, 12 grams ube extract
Beat the sourdough discard and egg yolk in until the sourdough discard is completely dissolved.
1 egg yolk, 75 grams sourdough discard
Switching to a spatula, stir in the dry ingredients until no traces of flour remain.
240 grams all-purpose flour, 14 grams ube powder, 1 teaspoon baking powder, ¼ teaspoon baking soda, 3 grams salt
Fold the white chocolate and macadamia nuts in until evenly distributed throughout the dough.
170 grams white chocolate chips, 70 grams macadamia nuts
Portion out cookie dough: Using a small cookie scoop (1 ½ tablespoon) portion out the dough and position cookie dough on parchment-lined baking sheet with room to spread (about 2 inches apart). You should be able to fit 12 cookies on each sheet. Top each cookie with more chocolate chips (optional).
Bake: Bake cookies at 350 for 12 minutes. Let the cookies cool on the baking sheet for at leat 5 minutes. Move cooled cookies to a cooling rack.
Enjoy and store: These cookies are best after they have cooled slightly. Store any leftover cookies in an airtight container at room temperature for up to 5 days.