1. Before you start – be aware that your kitchen machine will have a hard job here and has to knead a sticky dough for quite some time… be warned. You also cannot leave the machine alone – you have to check quite often or change the kneading speed so (all of) the dough is kneaded correctly ;P

2. Warm the milk until lukewarm and add to the bowl of your kitchen machine. Add the yeast and mix (e.g. with a rubber spatula) until dissolved completely. Mix in a tablespoon of the sugar and two tablespoons of the flour. Cover the bowl and let sit for about 30 minutes so the yeast can start working.

3. Add the remaining sugar, flour, the egg, and egg yolk, as well as the salt, and knead for about 8 minutes on medium-high speed until you get an elastic dough that pulls away from the sides of the bowl (it can still stick to the bottom). Reduce the kneading speed a bit and gradually add the butter while still kneading – make sure the butter you just added is fully incorporated before you add more. This will probably take about 4-5 minutes all in all. You might have to scrape down the sides from time to time and play a bit with the kneading speed of your kitchen machine. When all the butter is well incorporated continue kneading the dough for another 4-5 minutes. Your dough is ready when it’s crawling up your dough hook and only a small part of it is slightly sticking to the bottom of the bowl. Shape into a ball and place in a lightly greased bowl. Cover and place in the fridge for 2 hours.

4. Shortly before you are ready to continue with the babka, make the chocolate filling. Add half of the chopped chocolate to a microwave-safe bowl. Add the butter, liquor, heavy cream, and salt and warm up carefully in the microwave until the chocolate has melted completely and you got a nice thick chocolate sauce. Let cool down a bit.

5. For the streusels mix the flour, confectioners’ sugar, and salt in a small bowl. Add the vanilla extract and the butter and rub everything between your fingers to create the streusels. Place in the fridge until needed.

6. Line a 9×4 inches (23x11cm) loaf pan with baking parchment and grease lightly. Take the dough out of the fridge and roll out on a floured surface to get a 16×16 inches (40x40cm) square. Spread the chocolate all over the dough, sprinkle with the remaining chopped chocolate and chopped hazelnuts and then roll up tightly from one side. Cut the log lengthwise into two strings (showing the layers inside) and braid those two strings. It’s best to cut half of the log first to create the two strings, braid that, then cut the other side of the log and continue braiding. Tuck the ends underneath and place the babka in the prepared loaf pan.

7. Mix the egg white with sugar and salt. Brush the babka with the mixture – be generous. Sprinkle with the streusels and press them slightly down so they stick to the babka. Cover with some plastic wrap and let rise for 45-75 minutes. The babka should have expanded quite a bit, fill out the loaf pan and gone slightly over the edge of the pan.

8. While the babka is rising preheat the oven to 375° (190°C). Bake the babka for 45-50 minutes. If the top gets too dark (the exposed chocolate tends to get quite dark), cover with some baking parchment and continue baking. Take out of the oven, let cool down a moment in the pan, then remove by lifting the baking parchment and let cool down completely on a wire rack.