Place softened butter in a bowl and mix until smooth. Gradually add brown sugar in 2-3 batches and mix for about 1 minute.

Add room-temperature egg to the butter mixture in 2 batches, mixing gently until smooth.

Sift together the dry ingredients (baking powder, cinnamon powder, cake flour, misugaru powder) and salt, then fold into the wet mixture using a spatula.

Add chocolate chips to the mixture and lightly mix until just combined.

Divide the dough into two portions, wrap in parchment paper, and freeze for 1 hour.

Slice the chilled dough into 1cm thick pieces and bake in a preheated oven at 170°C for 12 minutes.