Put the sourdough starter with rye flour and water in a large bowl, mix everything together, cover, and leave to ferment overnight at room temperature.
The next morning, line a loaf tin with parchment paper. You will also need a plastic dough scraper and a bowl of cold water.
In another bowl, mix the rest of the rye flour, salt, spices, flax seeds, and psyllium husk. Pour hot water over the dry ingredients and mix with a wooden spoon. Transfer into the first bowl with your poolish and combine both mixtures. It will be quite sticky and messy but don't let that discourage you. Add some more water if needed.
Transfer the dough to a loaf tin. I help myself with a dough scraper which I dip in the water as needed. Smooth the surface of the dough, make sure there are no gaps inside, and sprinkle with rye flour. This way we will get a nice pattern after baking.
Cover the bread tin with a wet kitchen towel or plastic bag and leave it at room temperature for 3-4 hours. The bread should rise slightly (it will not double in size) and small cracks should appear on the surface of the dough.
Preheat the oven to 240 °C (464 °F). Place an old baking tray on the bottom of the oven and prepare a cup of water. Pour it into that pan at the bottom (watch out, steam will form), reduce the temperature to 220 °C (428 °F), and bake the bread for about 45 - 50 minutes, or until it gets a nice brown color and is fully baked.
After it's done, carefully take it out of the tin (watch out, it's very hot) and put it on the cooling rack to cool completely. Wait before slicing for at least 12-24 hours.