BABKA DOUGH

1. In a small bowl, combine the yeast, milk and 2 Tbsp of the sugar. Mix well, and leave to sit for 10-15 minutes, or until foamy.
2. In the bowl of a stand mixer fitted with the dough hook, combine the remaining 2 Tbsp sugar, rye flour, all-purpose flour, and salt. Mix briefly to combine. Add the eggs, vanilla, and foamy yeast mixture to the bowl. Mix on low for 2-3 minutes, until the dough is starting to come together. It may look slightly dry but do not worry - it will mix together nicely in the next steps. Increase the mixer speed to medium, and mix for another 10 minutes, until the dough is soft and smooth.
3. Reduce the mixer speed to low, and add the butter a little at a time, waiting until it is fully incorporated into the dough before adding the next piece. This process should take 3-4 minutes.
4. Once the butter is fully incorporated, increase the mixer speed to medium, and mix for a further 5 minutes, until the dough is very soft and smooth.
5. Transfer to an oiled bowl, and cover tightly with plastic wrap. Place in the fridge to rise - at least 3 hours and up to overnight (see notes)

CHOCOLATE ESPRESSO FILLING

1. Place the chocolate and butter into a medium heat proof bowl. Set over a pot of simmering water, ensuring that the bowl does not touch the water, and heat, stirring often, until the butter and chocolate have melted and the mixture is smooth.
2. Remove from the heat and add the salt, vanilla bean paste, espresso powder and powdered sugar, and whisk until smooth. Set aside to cool slightly, stirring occasionally.

ASSEMBLY AND BAKING

1. Lightly grease two loaf pans, and line with parchment paper.
2. On a lightly floured surface, roll the dough out to a 16" x 25" rectangle (40x64cm). Spread the chocolate filling over the surface of the dough. Starting with the long side, roll up into a tight spiral. Measure the length of the sausage of dough, then cut in half so it is in two sausages.
3. Place these pieces side by side on the lined baking sheet, cover with plastic wrap, and chill for an hour.
4. Remove the dough from the fridge. Using a sharp knife, cut the first piece in half, lengthwise, and then cross the pieces over each other, and then cross over two more times to form a twist, as shown in the photos (See my IG highlight).
5. Place into the loaf pan, tucking the ends under slightly if needed. Repeat with the second half of the dough.
6. Lightly cover the loaf pans in plastic wrap, and place in a warm place to rise for 45 minutes to an hour, or until the dough springs back lightly when pressed. While the loaves are proofing, preheat the oven to 350˚f / 180˚c.
7. Bake for 40-45 minutes, or until the loaves are golden brown and measure 190°f / 90°c on an instant read thermometer. While the loaves are baking prepare the sugar syrup - combine all the ingredients in a small saucepan and bring to the boil, then boil for 1-2 minutes. Leave to stand.
8. Remove from the oven and brush both loaves with the sugar syrup while hot. Allow to cool in pans for 15 minutes then remove and transfer to a wire rack and allow to cool completely before slicing.
9. Store leftovers in an airtight container, or wrap tightly before freezing.