Mix In a bowl milk and water and lightly heat them without exceeding 20°

Melt sourdough in the milk and water mixture.

Add the eggs and light beat the mixture.

In another bigger bowl combine flour, sugar and orange zestes

Pour the liquid mixture, little by little, in the dry mixture (flour and sugar) kneading with hands

Knead until you have a smooth and firm dough (you can transfer the dough on the work surface).

Add the 30gr of butter and knead until it will be completely absorbed.

Add salt and continue kneading until it will be incorporated.

Place the dough in a large lightly greased bowl and cover with plastic wrap. Leave the bowl at room temperature for a couple of hours then transfer in the fridge overnight (or at least for six hours).

After this time let the dough rest a couple of hours at room temperature.

Break chocolate and place into a heatproof bowl with the 120 gr of butter.

Sit over a pan of barely simmering water (a bain-marie) and allow the chocolate and the butter to melt, stirring occasionally.

When they're completely melted, remove from the heat and add the icing sugar stirring to have a smooth cream.

Let it cool

On a lightly floured working surface, roll out the dough until you have a 5mm high rectangle. From the short side it must be 30cm and the long side it ha to have a little less centimeters than the length of the circumference of the mold in which you are going to put it (I used a 24cm diameter mold, so the long side measured 70cm).

The calculation of the circumference is easily done (even for a dumm like me): multiply the diameter of the mold by 3.14. At the risult subtract five six centimeters which will be recovered with the leavening.

Once the dough is rolled out at the right measure, pour and spread the cold chocolate cream over the entire surface.

Roll the rectangle on the long side until it like a roulade. Wrap it in a lightly floured plastic wrap and put in the fridge for a couple of hours.

Use a sharp knife to gently cut the roll in half lengthwise, starting at the top and finishing at the seam, essentially dividing the log into two long even halves, with the layers of dough and filling visible along the length of both halves.

With the cut sides facing up, gently press together one end of each half, then lift the right half over the left half. Repeat this process, but this time lifting the left half over the right, to create a simple two-pronged plait.

Carefully lift the babka into a round pan with a heatproof little bowl so that the babka will not "crash" on itself during risen.

Let rise for a couple of hours.

Preheat oven at 160°.

Bake for 45'