On day 1, refresh your sourdough starter by combining 50g wholemeal flour, 50g wholegrain rye flour and 100g water with your sourdough starter.
On day 2, lightly toast the sesame seeds, then combine 200g of the refreshed sourdough starter from day 1 with the main dough ingredients in a large bowl.
Combine well to form a dough and knead for 10 minutes on a clean work surface.
Place the dough back into the bowl to rest for 1 hour at room temperature.
Give the dough another thorough knead, then shape and place into a large, lightly oiled loaf tin.
Leave to rest and rise until fully proven.
Preheat the oven to 220°C in time for baking, then bake for 10 minutes at 220°C before turning down the temperature to 180°C for another 50 minutes.
Cool on a wire rack.