On day 1, prepare the sourdough by combining 50g sourdough starter, 50g water and 50g wholemeal rye flour in a medium bowl. Cover the bowl and leave to rest at room temperature for 16-24 hours. Your refreshed starter will be full of bubbles and will rise considerably during that time.
On day 2, start by making a raisin mush. Combine 125g raisins and 375g warm water. Leave them to soak for at least 30 minutes. You can also soak them overnight if more convenient.
Next, combine all the dry ingredients in a bowl: 350g strong white wheat flour, 100g wholemeal rye flour, 50g rye flakes or oats, 10g salt and 2g cinnamon. Use a balloon whisk to mix the ingredients together well.
Strain the raisins, but keep the raisin water.
Add 100g of your sourdough and raisin water to your dry ingredients to form an evenly combined dough.
Knead for 10 minutes.
Place the dough back in the bowl, cover and leave to rest for 1 hour.
Add the raisins and fold in until evenly distributed throughout the dough.
Lightly flour the work surface, then shape the dough into a rectangular loaf - lots of the raisins will pop out on the dough surface, but that's ok and will make for a very nice look - dip it in flour all-round, so it doesn't stick, then place on a baking tray lined with baking paper to proof.
Cover with a moist (but clean) dish towel and leave to proof for 2-4 hours depending on your room temperature.
Preheat the oven to 210°C.
Bake in the centre of the oven for 45 minutes, or until the loaf is a good brown colour and the temperature is at least 93°C. I usually cover the top of the loaf with tin foil for the last 10-15 minutes to prevent the raisins from burning.
Cool on a wire rack.