Remove a ¼ teaspoon of yeast from the 10g packet and discard – if you use it all, the recipe contains too much yeast. (Cook’s note: it’s important to use an actual measuring spoon and not to try eyeball it with a normal teaspoon.) Add the remaining yeast in the packet to a large mixing bowl along with the flour, sugar and salt. Stir briefly to combine, then add the orange zest and soft butter and briefly work in. Next add half the milk and water and stir to combine. Add the chopped chocolate and gradually add the remaining water and milk as you mix. Tumble dough onto a very lightly floured surface. The dough will be incredibly wet and sticky at this point and you will be tempted to add more flour. Don’t! Kneed the dough for 7-10 minutes. As you work the gluten in the dough, the texture will change and it will become smooth and much firmer.
Place dough ball in a large bowl lightly painted with vegetable oil, cover with cling film and leave to prove for 60-90 minutes until the dough ball has doubled in size. Knock dough flat, divide into three equal pieces and roll three long sausages. Place them next to each other, squeeze dough sausages together at one end and start plaiting (like you would braid a ponytail). Tuck the ends in neatly underneath. Place loaf on a baking sheet lined with baking paper and allow it to prove for another hour until it has doubled in size.
Once the loaf has doubled in size, brush it with the egg wash and bake until golden for 25-30 minutes in a preheated 190-degree Celsius oven. Insert a thin skewer into the bread. If it comes out clean, your tsoureki is done. Allow too cool slightly, then place dollops of the melted chocolate in the folds of the tsoureki and nest the candied eggs in the melted chocolate to secure. Slice and eat as is or spread over decadent salted butter. This is best on the day it is made. Use the leftovers to make a gorgeous bread and butter pudding!
(If you want to make a caraway and cranberry tsoureki instead: Add a heaped tablespoon of caraway seeds, leave out the chocolate and add two thirds of a cup of roughly chopped dried cranberries instead. Boil 3-5 eggs in water containing loads of red food colour until hard, allow to cool, then push them halfway into the folds of the dough just before the loaf goes into the oven.)