Combine the flour, cocoa powder, sugar, instant yeast, and salt. Add the lukewarm milk and egg, then knead until a rough dough forms. Add the softened butter gradually and knead for 8 to 10 minutes, until the dough is smooth, elastic, and only slightly tacky.

Place the dough in a lightly greased bowl, cover it, and let it rise in a warm place for 60 to 90 minutes, or until doubled in size.

Divide the risen dough into three equal pieces. Roll each piece into an approximately 8-inch or 20-cm circle. Warm the chocolate-hazelnut spread very briefly if it is too stiff to spread.

Place one dough circle on parchment and spread it with half of the hazelnut spread, leaving a 1-cm border. Add the second circle, spread with the remaining filling, and top with the third circle.

Set a small glass or cookie cutter in the center as a guide. Cut the stacked dough into 16 equal strips from the edge of the glass to the outside edge, pair adjacent strips, twist each pair twice in opposite directions, and pinch the ends together.

Transfer the shaped loaf on its parchment to a baking tray. Cover loosely and let it proof for 30 to 45 minutes, until slightly puffy.

Brush the loaf lightly with beaten egg. Bake at 180°C/350°F conventional or 170°C/340°F fan for 25 to 30 minutes. If the bread darkens too quickly, cover it loosely with foil.

Cool the bread for at least 20 minutes. Pipe 3 to 5 concentric circles of melted white chocolate over the top, drag a toothpick or skewer from the center outward at regular intervals, and add a dark-chocolate spider if desired.