For the dough, place the flour, castersugar, yeast, and lemon zest in a stand mixer fitted with the dough hook and mix on low speed for 1 minute. Add the eggs and half a cup water and mix on low speed for a few seconds, then increase the speed to medium and mix for 3 minutes, until the dough comes together. Add the salt and then start adding the bbutter, a few cubes at a time, mixing until it is incorporated into the dough. Continue mixing for about 10 minutes on medium speed, until the dough is completely smooth, elastic, and shiny.

Place the dough in a large bowl brushed with sunflower oil, cover with plastic wrap, and leave in the fridge for at least half a day, preferably overnight. Or on the bench if cool.

Grease two 2¼-lb / 1kg loaf pans (9 by 4 inches / 23 by 10 cm) with some sunflower oil and line the bottom of each pan with a piece of waxed paper. Divide the dough in half and keep one-half covered in the fridge.

Make the filling by mixing together the icingsugar, cocoa powder, chocolate, and meltedbutter. Let it cool until it's a spreadable paste not too runny.

Roll out the dough on a lightly floured surface into a rectangle measuring 38 by 28 cm or the length of the baking tin-ish. Spread half the chocolate mixture over the rectangle, leaving a 2cm border all around. Sprinkle half the nuts on top of the chocolate, then sprinkle over half the extracastersugar.

Brush a little bit of water along the long end farthest away from you. Use both hands to roll up the rectangle like a roulade, starting from the long side that is closest to you and ending at the other long end. Press to seal the dampened end onto the roulade and then use both hands to even out the roll into a perfect thick cigar. Rest the cigar on its seam.

Trim ends of the roulade with a serrated knife. Now use the knife to gently cut the roll into half lengthwise, starting at the top and finishing at the seam. You are 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, and then lift the right half over the left half. Repeat this process, but this time lift the left half over the right, to create a simple, two-pronged plait. Gently squeeze together the other ends so that you are left with the two halves, intertwined, showing the filling on top.

Carefully lift the cake into a loaf pan. Cover the pan with a wet tea towel and leave to rise in a warm place for 1 to 1 ½ hours. The cake will rise by 10 to 20 percent. Repeat the whole process to make the second cake.

Preheat the oven to 190°C, making sure you allow plenty of time for it to heat fully before the cakes have finished rising. Remove the tea towels, place the cakes on the middle rack of the oven, and bake for about 30 minutes, until a skewer inserted in the center comes out clean.

While the cakes are in the oven, make the syrup. Combine ⅔ cup (160ml) water and whitesugar in a saucepan, place over medium heat, and bring to a boil. As soon as the sugar dissolves, remove from the heat and leave to cool down. As soon as the cakes come out of the oven, brush all of the syrup over them. It is not important to use up all the syrup, but use at least half. Leave the cakes until they are just warm, then remove them from the pans and let cool completely before serving.