Prepare a yeast dough and let it rise once (see Easter yeast plait). In the meantime mix the poppy seed filling with the jam and line a baking tray with baking paper.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Knead the dough well on a floured work surface, then roll out into a rectangle (35 x 50 cm). Spread the poppy seed mixture evenly on top, leaving a margin of approx. 2 1⁄2 cm on one short side.
Roll up from the other short side. Carefully place diagonally on the baking tray. Cut the roll open with a floured knife and lay it into a cord.
Whisk the egg yolk and 2 tablespoons of water. Gently brush the poppy seed cord with it. Bake in the hot oven on the lower shelf for about 40 minutes. After about 25 minutes baking time, cover the cord with aluminium foil if necessary.
Remove and let it cool down. Then dust with icing sugar.