In a bowl, combine softened unsalted butter, icing sugar, and salt. Whisk until smooth.
Add the egg, one-third at a time, to the mixture, whisking until combined before adding more.
Sift the all-purpose flour and black sesame powder into the mixture. Mix until a dough is formed. Cover the dough with plastic wrap and place it in the freezer for 30 minutes.
Preheat the oven to 130°C (266°F). Line a baking sheet with parchment paper or a silicone baking mat.
Roll the dough out to a 3mm thickness. Lightly dust the rolled-out dough with flour. Using a cookie cutter, cut the dough into shapes. Re-roll the remaining dough and continue cutting until all the dough is used.
Bake for 30-32 minutes. These cookies won’t change color, so carefully flip one over to check if it is fully cooked.
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