Whisk buttermilk and egg. Mix flour, baking powder, baking soda, sugar and salt. Cut butter into cubes and add to the flour mixture. Mix quickly with your fingertips to a coarse crumbly dough.
Briefly stir in the peanuts, chocolate and buttermilk and egg mixture. Stir only until just enough to form a dough.
Form dough into 2 balls. Roll each ball into a circle (approx. 15 cm Ø) on a floured work surface. Cut the circles into six with a knife. Place the pieces on a baking tray lined with baking paper.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 10-12 minutes. Remove and let cool on a cake rack. Dust with icing sugar.