Place all of the ingredients for the light dough except the water into a bowl and all of the ingredients for the dark dough except the water into a separate one. Gradually add the water to each bowl, mixing until it forms a soft, slightly sticky dough; you may not need to add all of the water or you may need a little more.

Turn each dough out onto an un-floured surface and knead for about 10 minutes or so until they are smooth and elastic. Shape each dough into a ball and place in a lightly oiled bowl, cover, and leave to rise until doubled in size, about 1.5 hours.

Grease an approx 28x13cm (11x5in) loaf tin (or you can just bake the loaf on a baking sheet). Punch down each dough and knead very briefly then divide each dough into 2 equal pieces. Roll each piece of dough out on a lightly oiled surface into a square about 20cm (8in) wide; stack the squares of dough on top of each other light then dark then light then dark; roll the stack out gently until it is about 27cm (10.5in) square then roll it up tightly into a log.

Place the log seam side down in the loaf tin or on a baking sheet and cover loosely with oiled clingfilm. Leave to rise until doubled in size, 1-2 hours; meanwhile, heat the oven to 180C/350F/gas mark 4.

Just before you place the loaf in the oven, cut several deep slashes across the top of the loaf, brush it with a bit of milk and scatter over a few caraway seeds if you like. Bake for 45-55 minutes until the loaf is well-risen and sounds hollow when tapped on the bottom, the internal temperature should reach 94C/200F.

Turn the loaf out onto a wire rack and leave to cool completely before slicing.