In a small saucepan, combine granulated sugar and water over medium heat. Bring the mixture to a boil, stirring occasionally until the sugar completely dissolves, which should take about 3-5 minutes. Remove from heat and allow the syrup to cool; refrigerate until ready to use.

In your stand mixer, combine whole milk, sour cream, sugar, and fresh or dry yeast. Mix gently on low speed for 1-2 minutes until blended. Gradually add all-purpose flour, then salt, and room temperature unsalted butter, kneading on medium speed for 8-10 minutes until the dough is smooth and elastic.

Once your dough reaches the desired smoothness, shape it into a ball and place it in a greased bowl, covering it with a damp cloth. Let it rise undisturbed for about 1 hour or until it doubles in size.

In a small saucepan, melt bittersweet chocolate and unsalted butter over low heat, stirring until smooth. Remove from heat and whisk in cocoa powder, powdered sugar, and vegetable oil until you achieve a silky texture.

After the first rise, punch down the dough gently and transfer it to a floured surface. Roll it out into a rectangle roughly 12x18 inches. Spread the cocoa filling evenly over the surface, then carefully roll the dough back up from one long end.

Next, spread Nutella over the rolled dough, fold it into thirds, and roll out again until it resembles a log. Cut strips of the dough, twisting them gently to create beautiful shapes.

Arrange the twisted pieces in a greased baking pan, leaving space for expansion. Cover the pan with a clean kitchen towel and allow the shaped dough to rise for another 30-35 minutes.

Preheat your oven to 170°C (340°F). Once the dough has risen, place it in the oven and bake for 40-45 minutes.

As soon as your Cocoa and Nutella Yeast Cake is out of the oven, brush the top generously with the cool sugar syrup.