Measure softened butter and peanut butter into a bowl.

Whisk the butter and peanut butter until smooth.

Add 60g of brown sugar and mix lightly without dissolving the sugar completely.

Quickly mix in the egg, then add the remaining brown sugar and combine.

Sift cake flour, baking powder, and baking soda into the mixture and fold until no dry flour is visible.

Shape the dough into a log, wrap in plastic wrap, then parchment paper, and chill in the freezer for 2 hours.

Slice the dough into 1.5cm thick pieces and space them out on a baking tray.