Make the dough: Mix flour, yeast, sugar and salt. Add warm milk and eggs and knead until a dough forms.
Add the softened butter gradually, kneading until the dough is smooth and elastic, about 8–10 minutes.
Cover and let rise for 1½–2 hours, or until roughly doubled.
Make the filling: Melt the chocolate and butter together. Stir in icing sugar, cocoa, vanilla and salt. Cool until spreadable.
Roll the dough into a rectangle, approximately 40 × 30 cm. Spread the chocolate filling evenly over it.
Roll it tightly from the long side into a log. Cut the log lengthwise down the middle to expose the layers.
Twist the two halves together, keeping the cut sides facing upward. Chocolate Babka Recipe
Place in a greased 23 × 13 cm loaf tin. Cover and let rise for another 45–60 minutes.Chocolate Babka Recipe
Bake at 180°C for about 35–45 minutes, until deeply golden and cooked through.
Make the syrup: Simmer sugar and water for 1–2 minutes. Brush generously over the hot babka.
Cool for at least 20–30 minutes before slicing.