Yield: about 5 dozen cookies
Whisk together flour, black sesame flour, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream together butter and coconut oil. Once smooth, add sugar and powdered sugar.
Add dry mixture and mix on slow speed. Add egg yolks one at a time and mix until dough comes together.
Scoop dough out of a bowl, divide into two equal parts and flatten gently into two rectangles. Wrap in plastic wrap and let chill in the fridge for 30 minutes (up to overnight).
Preheat oven to 350 degrees F. Line baking sheets with parchment paper.
Remove shortbread dough from the fridge. If dough is too cold, allow to warm up slightly until dough is pliable. Roll out dough to a thickness of about 1/2-inch. If dough is too cold and starts to crumble while you roll, simply warm up the dough with your hands and press it into a ball. Once dough is pliable, re-roll. Use a lightly floured fluted 2-inch round cookie cutter to stamp out cookies. Ball up any scrapes and re-roll as necessary.
Place cookies on prepared baking sheet at least 1-inch in apart. Bake for 15-17 minutes. Allow to cool in pan for 3 minutes before transferring to a wire rack to cool to room temperature.
Hibiscus Glaze: Bring water to a boil. Add dried hibiscus flowers. Allow to steep for 5-8 minutes until tea is super dark red. Place sifted powdered sugar in a medium bowl. Add 3 Tbsp of hibiscus tea to powdered sugar. Stir until mixture is smooth. Dip cookies into hibiscus glaze or drizzle glaze over cookies and top with black sesame seeds.