DAY 1

Feed Sourdough Starter:

• 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 the 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 4-5 minutes).
• 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 8-10 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 two hours, every 30 minutes, perform 3-4 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 hours. 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 and Shaping:

• Line a 2-lb loaf tin with baking parchment.
• The next step is the trickiest one, but dust the surface with flour and work quickly to take advantage of the cold and stiff dough from a night in the fridge.
• Scoop the dough onto a floured work surface. Roll it out into a large rectangle measuring about 30x40cm (12×16 in).
• ​Spread the pesto all over the surface, scatter grated parmesan and sun-dried tomatoes, then roll it into a very tight roll starting from the long side.
• ​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. The filling may fall out, and the layers may start falling apart, but don't hesitate and just go for it. You can poke whatever bits fallen out back in later.
• Place it into a prepared loaf tin (make sure to fit it in snugly and don't worry if you have to serpentine the braid on top for a second layer). Poke any exposed sundried tomatoes deeper into the loaf to prevent them from burning.

Second Proof:

• 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 20-25% in that time.

Baking:

• Preheat the oven to 170°C Fan (340℉).
• Make an egg wash by mixing an egg yolk with a teaspoon of milk. Brush it on the surface of the babka gently. Scatter flaky salt on top.
• Bake Sourdough Babka in the oven for 40-50 minutes. It should puff up heaps and turn golden brown on top. The internal temperature of your pesto babka should reach 90–93°C / 194–200°F.
• We recommend cooling in the tin for 10–15 min before transferring to a rack to prevent the loaf from collapsing.