Whisk softened butter with sugar and salt.
Add egg and mix.
Add flour and knead (with hands).
Place in fridge for 1 hour.
Roll out the dough in rectangular form (on floured surface).
Spread peanut butter evenly and roll firmly.
Wrap in plastic film and place for 1 hour in freezer (in two halves).
Cut in slices (1/2 cm) and put on baking tray. (with baking paper)
Bake in preheated oven at 160° C for 15 minutes.