Cream butter, sugar and egg with the whisk of the mixer. Mix 250 g flour, baking powder and cocoa. Stir in portions briefly. Knead the dough well on a floured work surface. Roll out approx. 3 mm between two layers of baking paper.
Put the dough plate in a cool place for about 30 minutes.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line two baking trays with baking paper. Cut out approx. 40 circles (approx. 6 cm Ø) from the dough sheet and place them on the baking trays with a distance of approx. 3 cm between them.
Bake in a hot oven for 8-10 minutes, sheet by sheet. Take out and let cool down.
Place half of the biscuits on a baking tray with the underside facing upwards. Cut the marshmallows in half crosswise with scissors. Cover each cookie with one half of the marshmallow with the cut surface facing down. Bake for about 2 minutes in a hot oven at the same temperature.
Spread the remaining biscuits on the underside with 1⁄2 TL jam. Take marshmallow biscuits out of the oven and immediately press 1 jam half on each. Let the biscuits cool down.
Roughly chop the chocolate coating. Melt in a hot water bath. Cover the biscuits completely with this and let them dry on a cake rack.