Melt butter and peanut butter together in a saucepan over low heat. Add sugar and stir until combined. Do not boil.

Let the melted mixture cool. Meanwhile, crush nuts into small pieces.

Add egg yolk to the cooled mixture and stir until it becomes sticky like caramel.

Sift flour into the mixture and combine until a dough forms. Add crushed nuts and mix well.

Shape the dough into a log, wrap in plastic, and freeze for 20 minutes.

Slice the dough into small pieces and shape each piece into a cookie. Let them rest for 5 minutes.

Bake cookies at 180°C (356°F) for 15-20 minutes. Check periodically to avoid overbaking.