Whip softened butter until it reaches a mayonnaise-like texture.

Add powdered sugar to the whipped butter and mix until smooth.

Add egg yolk in two batches and mix well.

Sift and add the dry ingredients (cake flour and cocoa powder) to the mixture.

Mix the dough until it starts to form a cohesive texture.

Add almond slices to the dough and gently mix.

Shape the dough into a log and freeze it to firm up.

Slice the frozen dough into cookie shapes.

Bake the cookies in a preheated oven at 170–180°C for 10–15 minutes.