Sift the flour, sugar, and cinnamon into the bowl of a stand mixer. Add the yeast and mix to combine.

Add the eggs and milk, and beat on low speed for 2 minutes until the mixture comes together. Increase to medium speed and knead for about 5 minutes.

Add the salt, then gradually incorporate the softened butter pieces while mixing continuously. The dough should become soft, glossy, and pull away from the sides of the bowl.

Transfer the dough (seam side down) to a greased bowl, brush lightly with melted butter, cover, and refrigerate overnight.

Prepare the filling by mixing the cocoa powder, powdered sugar, melted chocolate, and butter in a bowl until smooth and spreadable. Let it sit briefly to firm up slightly.

Butter two small loaf pans and line their bases with parchment paper.

Divide the dough into two equal portions. Roll out one portion into a rectangle (about 30 x 40 cm).

Spread half of the filling evenly over the surface, leaving a 1.5–2 cm border around the edges.

Sprinkle with half of the chopped walnuts and a light dusting of sugar.

Roll the dough tightly from the long side into a log, then slice it lengthwise down the middle.

Place the two halves side by side, cut sides facing up, and twist them together into a braid. Press the ends to seal and transfer to the prepared pan.

Repeat the process with the second portion of dough.

Cover the pans with a damp towel and let the dough rise in a warm place for 1½–2 hours, until doubled in size.

Preheat the oven to 180°C (fan). Bake on the middle rack for about 30 minutes, until golden brown and fully risen.

While still warm, drizzle with some syrup to give the babka a glossy finish and extra moisture.

For the Syrup

Bring all the syrup ingredients to a boil over medium heat for 2 minutes. Let it cool slightly before using.