In a glass bowl combine warm milk and 1 tablespoon of granulated sugar. Sprinkle yeast over the mixture and let it sit for about 5-10 minutes until foamy.
To a standing mixer combine flour, remaining ½ cup of sugar and salt. Attach the dough hook and start mixing on a low speed.
Add the yeast mixture and mix slowly until well combined.
Gradually add the eggs and egg yolk one after another and start kneading the dough on a medium speed.
Add the butter a tablespoon at a time and reduce the speed to low and knead all the butter cubes are fully incorporated and mixing until a soft dough forms. It will take about 7-8 minutes to form a complete dough.
Place the dough in a greased bowl, cover with plastic wrap, and let it rise in a warm place for about 1-2 hours or until doubled in size.
Meanwhile prepare the cinnamon filling: In a bowl, combine unsalted butter, light brown sugar and ground cinnamon. Mix until smooth and creamy and set it aside.
Once the dough has doubled in size, punch it down and divide it into two equal parts.
Roll out each dough portion into a rectangle on a floured surface, about 9X13 inches.
Spread half of the cinnamon filling evenly over each rectangle, leaving a small border around the edges.
Starting from the long side, tightly roll up each rectangle into a log.
Cut each log in half lengthwise, exposing the layers of chocolate filling.
Place them one above the other like a “X” and start twisting the two halves together, then transfer the twisted dough into a greased loaf pan lined with parchment paper.
Cover the pan with a kitchen towel and let the babka rise for another 1-2 hours.
Preheat your oven to 350°F (175°C).Once the babka has risen, bake it in the preheated oven for 35-40 minutes until golden brown and cooked through.
Meanwhile prepare the sugar syrup; Combine water and granulated sugar in a small saucepan over medium heat. Cook until the sugar dissolves, then brush the syrup over the warm babka as soon as it comes out of the oven.
Allow the babka cool in the pan for 10-15 minutes, then transfer it to a wire rack to cool completely before slicing and serving.
Notes
Nutrition information based on 1/12 of 1 loaf of babka.