In a large glass bowl, combine active sourdough starter, wholemeal rye flour and half of the warm water (150 g / 5.3 oz).

Mix into a thick paste, scrape the sides of the bowl, smooth the top with a spatula and cover with a kitchen towel. Leave to ferment in a warm place overnight or until the preferment has risen and is bubbly throughout.

Brush your baking tin with a little oil and coat it with either of the flours. If your tin isn't non-stick, you may want to add a sling of baking parchment in the middle of the tin for easy removal.

To the bowl with prefermented starter, add wholemeal wheat flour, the other half of water, salt and sunflower seeds (hold some back for the topping). Mix really well, until no flour pockets remain.

Transfer the dough into the prepared baking tin, pressing the mixture down in the tin so that it's evenly distributed and there are no air pockets.

Smooth the top with a wet hand or a wet spatula. Cover with an upside down bowl and set aside for 2-4 hours in a warm place, until the bread rises and domes out of the tin.

Pre-heat the oven to 220° C / 430° F.

Once the bread has risen, handle it gently. Gently spray the top with water and sprinkle with some sunflower seeds.

Place the bread on the middle shelf. Optionally, place a deep baking tray filled with warm water at the bottom of the oven.

Bake for 15 minutes, then decrease the temperature to 200° C / 390° F and bake for further 55-60 minutes.

Once baked, take the bread out of the tin and place it on a drying rack to cool.

Allow the bread to settle overnight or until stone-cold before cutting into it.