Put half the rye flour, half the white flour and all the yeast into a large bowl, then add about 175 ml/6 fl oz of water and mix well until you have a thick paste.

Leave this dough in the bowl overnight for 10–12 hours.

Add the rest of the flours, the salt, butter, caraway seeds and remaining water and mix well in the bowl for 3 minutes.

Tip out onto a lightly floured surface and knead well for 3 minutes, then put the dough back in the bowl and leave to rise for 1 hour.

Line a baking tray.

Tip the dough out onto your floured surface and roll into a ball, then, using a rolling pin, flatten it slightly into a disc.

Cover the top with rye flour, put the dough on the baking tray and leave to rise for 2 hours.

Preheat the oven to 220°C/425°F/gas mark 7.

Bake the loaf for 30 minutes, then serve warm with smoked salmon.