In a small saucepan, combine granulated sugar and water over medium heat. Stir until fully dissolved, about 3-5 minutes, then remove from heat and chill.

In a stand mixer bowl, mix warm milk, sour cream, sugar, egg, and yeast at low speed for 2 minutes. Gradually add flour and salt, then add softened butter. Knead for 10 minutes.

Cover the dough with a towel and let it rise in a warm area for about 1 hour until doubled in size.

Melt bittersweet chocolate and butter together until smooth, then whisk in cocoa powder, powdered sugar, and vegetable oil.

Punch down the risen dough, divide into two portions, roll each into a rectangle, spread filling, fold, and roll again. Spread Nutella on top.

Slice the dough into 4cm strips, twist or tie into shapes, and place in a prepared baking pan.

Cover and let the dough rise again for about 35 minutes.

Preheat the oven to 170°C (340°F) and bake for approximately 45 minutes until golden brown.

Brush the warm cake with cold sugar syrup immediately after baking.