Day 1:
75g sourdough starter
140g water
100g rye flour
Combine the first two ingredients well, then add the flour. Stir to combine then cover with shower cap/towel etc overnight, between 12 and 24 hours.
Day 2:
Add to the leaven –
175g rye flour
7g sea salt
125g water (room temp)
10g caraway seeds, if liked
6g molasses. It's night on impossible to get only 6g out of a tin of molasses; it's like lava. Just chuck in a good glug. You'll be able to adjust the more you make the bread, depending on how you like the taste.
Method
Grease and line a 500g loaf tin with baking parchment. It's much easier to take the bread out of the tin after it's cooked this way.
Fill the tin with the flour mixture, smoothing it flat with a palette knife. Sprinkle rye flour on the top. Leave out at room temperature until cracks start to form (it could take two hour depending on how warm your kitchen is, or the time of year) then put it in a pre-heated oven at 200C fan/220C non-fan/425F/gas mark 7.
Leave in oven for roughly 40 minutes (turning 180 degrees if your oven has a hot spot), then remove from tin, remove the parchment, and turn it upside down so the bottom bakes. This could take a further 10-20 minutes. Tap the bottom and if there's a hollow sound it;s done. Place on a wire rack to cool then wrap in baking parchment (you won;t bother doing this step but it'll be OK) and leave for 24 hours before slicing. Seriously, leave it 24 hours. The taste will mature over the next few days.
*adapted from a recipe on swedishfood.com