In a small saucepan, combine equal parts granulated sugar and water over medium heat. Stir until the sugar is fully dissolved, about 2-3 minutes. Once dissolved, remove from heat and allow the syrup to cool completely before refrigerating it.

In a stand mixer bowl, combine warmed whole milk, sour cream, sugar, yeast, and flour. Mix on low speed until combined, then add salt and softened unsalted butter. Increase speed to medium and knead the dough for about 10 minutes until it’s smooth and elastic.

After kneading, shape the dough into a ball and place it in a lightly greased bowl. Cover it and set it in a warm area to rise for about 1 hour.

While the dough is rising, prepare the cocoa filling by melting bittersweet chocolate and unsalted butter. Whisk in cocoa powder, powdered sugar, and vegetable oil until smooth. Set aside.

Once the dough is risen, punch it down and divide into two pieces. Roll each into a rectangle, spread cocoa filling on one, fold, then spread Nutella on top. Cut and twist the dough, place in a greased baking pan.

Cover the assembled cake loosely with a towel and let it rise again for 35 minutes.

Preheat your oven to 170°C (340°F). Bake for approximately 45 minutes until golden brown and a toothpick comes out clean.

Brush the warm cake with the chilled sugar syrup immediately after removing from the oven. Let it cool slightly before transferring to a wire rack.