DAY 1

• First thing in the morning, feed your sourdough starter and leave it in a warm spot to at least double in volume. We typically feed our starter in a ratio of 1 part starter: 1 part water: 1 part flour, and it doubles (or even triples) within 4 hours.

The Dough:

• In a bowl of a stand mixer, mix the flour, sugar and salt. Add the milk, eggs and active sourdough starter. Start mixing the dough with a bread hook attachment on low speed until you have a shaggy dough (about 5-7 minutes). Cover the bowl with a tea towel and let the dough rest for 10-15 minutes.
• Return the bowl to your stand mixer, and running it on medium speed, start adding room temperature butter one bit at a time. Note, that butter will tend to stick to the sides of the bowl, so you may need to scrape the sides once or twice. Run the mixer for 10-15 minutes until you have a relatively wet, but soft and elastic dough that passes the windowpane test.

Bulk Fermentation and Coil Folds:

• Scoop the dough into a lightly greased bowl, cover it with plastic wrap and leave it in a warm spot (20-24°C) for 4 hours.
• Over the first hour, every 30 minutes, perform 2 series of coil folds. You will have a much less sticky dough by the end of the fourth coil fold. Then leave it to finish its first rise for 2-4 hours, depending on the temperature, to finish bulk fermentation. Your dough is unlikely to double in size, but should increase by about a quarter.

Cold Proof:

• Place the sourdough babka dough in the fridge to finish proofing overnight. The dough ferments slower at cold temperatures, so it can safely stay in the fridge for 8-24 hours.

DAY 2

Filling:

• Heat butter and cream in a small pan over low-medium heat until melted. Add the finely chopped chocolate and mix until it melts, then remove the pan off the heat.
• Whisk in the cocoa powder and powdered sugar - make sure no dry lumps remain. Allow the mixture to cool for about 45 minutes, until it thickens to a spreadable consistency.

Shaping:

• Line a 2 lbs loaf tin with baking parchment.
• Scoop the dough onto a floured work surface. Roll it out into a large rectangle measuring about 20x40cm (8×16 in).
• Spread the chocolate filling across the surface, then roll it into a very tight roll starting from the short side and pinch the seam together.
• Cut the roll in half lengthways using a sharp knife, but leave it intact at one end (so you have two legs attached at the top).
• Twist the two legs together. Then place it into a prepared loaf tin.

Second Rise:

• Brush a piece of plastic wrap (cling film) with neutral oil. Cover the top of the sourdough babka loosely and leave it at a warm temperature (21-27°C) to proof again for 2.5-3 hours. The loaf should puff up by about 25% - it will not double.

Baking:

• Preheat the oven to 180°C Fan (360℉).
• Bake Sourodugh Babka in the oven for 40-50 minutes. It should puff up heaps, be golden brown on top.

Sugar Syrup Glaze:

• As the babkas bake, make the sugar syrup by combining the sugar and water in a small pan. Simmer until the sugar dissolves, then remove from heat.
• As soon the as the babka comes out of the oven, brush the top with the sugar syrup.
• Allow the sourdough babka to cool in the loaf pan for 20-30 minutes, then remove and place on a wire rack. Best served slightly warm or at room temperature.