Rúgbrauð — dark Icelandic rye bread

Preheat the oven to 100°C, conventional top and bottom heat. Prepare an ovenproof loaf tin with a capacity of about 2 l and an ordinary baking lid. Line the base and sides with baking paper. Instead of a lid, you can use two layers of aluminum foil with room above the batter. Do not use a pressure seal. Do not grease the tin.

Put all the rye flour and wheat flour, the baking soda and salt into a large bowl. Mix thoroughly with a whisk or spoon, breaking up any lumps of baking soda and distributing it evenly through the flour. All the weighed flour goes into the batter; do not set any aside for dusting.

Weigh the kefir and golden syrup into a second bowl. Stir with a spoon until the syrup blends into the kefir. Scrape it thoroughly from the sides of the bowl. Do not dilute the mixture with water, and do not grease the bowl with any extra fat.

Pour the kefir and syrup into the dry ingredients. Mix briefly but thoroughly until no dry flour remains and you have an even, thick, sticky batter. Do not knead it, and do not leave it to rise. Immediately transfer all of it to the prepared tin, scraping the bowl with a spatula. Level the top. The batter should fill no more than two thirds of the tin's height. Cover with the lid or prepared foil, leaving room for it to rise.

Place the covered tin on the middle level of the oven and bake for about 11–12 hours at 100°C. Do not remove the cover during baking. Towards the end, the bread should be distinctly dark and firm; a skewer inserted into the center may have moist crumbs on it, but no raw, pasty batter. If the center is still pasty, cover the tin and bake for longer, checking again after about 30 minutes.

Remove the tin from the oven and carefully take off the cover, watching out for steam. After about 15 minutes, lift the bread out by the paper and transfer it to a wire rack. Pull the paper away from the sides and leave the loaf to cool completely, about 4 hours in total from taking it out of the oven. Only cut the loaf into thin slices with a sharp knife once cold. Divide it into fourteen portions of one or two slices each; the moist, fine crumb should stay compact.

Put the completely cooled bread into a container with a lid or wrap it thoroughly. Store in the fridge and use within 3 days. If you do not need the whole loaf, freeze some of it in portions, separating them with baking paper so that you can easily take out the amount you need.