Cream together butter and sugar. Add salt and all purpose flour until you get a crumbly mixture. Divide into two bowls, about 170g each.
In one bowl, mix in kinako. In the other, the black sesame powder
Gather the kinako dough and pack it in your hands. It will be crumbly at first but will start holding its shape. Do the same with the back sesame dough.
Preheat oven to 350F. Line a baking sheet with parchment or a baking mat
Roll out the kinako and the sesame dough into a rectangular log, about 1.5" tall and about 1.5" wide. Press the two logs together for a dimension that is 1.5" tall and 3" wide. Using a rolling pin, gently roll the top of the logs to fuze the dough together and even out the top. Use a knife and slice 1/4" pieces and placing them flat on a baking mat or parchment paper. Repeat until done. Then using a fork, make holes on the face of the shortbreads.
Bake for 10 minutes or until the edges are just turning brown. Remove and let cool on the baking sheet for 15 minutes before transferring to a cooling rack.