Preheat your fan oven to 160°C (325°F) or 175°C (350°F) if you're not using a fan oven. Grease and line with parchment paper (for easier handling later) a 9x5 or 10x5 inch (25x12 cm) loaf tin.
In a bowl of a stand mixer sift together flour, salt and sugar. Set aside while you prepare the rest.
If you're using active dry yeast (like me), you need to activate it first. Heat your milk and water over a medium heat until it reaches about 50°C. Put active dry yeast in a small bowl and cover with a couple of tablespoons of that warm milk and water mixture and a teaspoon of sugar. Mix it with a teaspoon and leave it to rest for 5 minutes or until it becomes all frothy and bubbly on top.
Cut your butter into cubes and set aside.
Once you got everything ready, pour your yeast and milk/water mixture to the flour. Add three eggs. Using your stand mixer fitted with the dough hook, knead it on low-medium speed for about 10-15 minutes or until it starts pulling from the sides and is elastic.
With the mixer still running, add the butter one cube at a time and mix until fully incorporated into the dough. Then continue mixing for a further 10-15 minutes or until it's elastic and no longer sticking to the bowl. On a lightly floured surface, knead the dough a little bit to form a ball and place into a lightly greased bowl. Cover with cling film and let it rise slowly in the fridge, overnight or up to 48 hours.
for the chocolate filling
Place all of the ingredients into a medium bowl and melt it over a bain marie (a pan of simmering water), stirring with a whisk occasionally until it all melts and incorporates.Set aside and let it cool and thicken slightly while you prepare the dough.
Remove the dough from the fridge onto a lightly floured surface and divide into two equal sized pieces. Using a floured rolling pin, roll out each piece (one at a time) into a rectangle roughly 30x40cm (17x12 inch).
Using a small offset palette knife, spread half of the chocolate mixture all over the dough, leaving a small border around the outside. Roll the dough, along the long edge, into a tight log.
Using a very sharp knife cut through the middle, cutting the dough into two long pieces. Place one piece of dough over the second forming an "X" then braid together the two pieces of dough.
Gently place the babka into the prepared loaf pan. Cover the pan with cling film and place in a warm place for about an hour and a half to two hours or until the dough has about doubled in size. Repeat with the second piece of dough. *You can leave the other babka to rise in the fridge overnight, so you can have it fresh the next day.
When your babka has risen, bake it in a preheated oven for about 35 minutes or until golden brown on top.
for the syrup soak
While the babka is baking, prepare the sugar syrup for soaking. Place sugar and water in a small saucepan and bring to a simmer. Once the sugar has fully dissolved, turn off the heat and set it aside until you need it. *This is enough for two loaves.
Once the babka is done, brush it liberally with the sugar syrup. Use all the syrup (half for each babka), the babka will soak it up although you'll think it's too much. It's not, trust me.
Leave the babka to cool completely before cutting it, to avoid being doughy and dense.
Not all ovens are the same. If you experience browning at the top and are afraid it's too much, put a baking paper sheet over it or cover in aluminium foil. Just be careful when pulling the pan out of the oven - aluminium foil gets really hot!
They are best eaten the same day. I suggest keeping them in an airtight container if you wish to eat them the next day as well. If you don't have an airtight container, tightly wrapped cling film would also do the trick.
If you still don’t own one, I advise you to buy a kitchen scale – they’re cheap and easy to use, and always guarantee the same results in baking!