Warm up milk to about 40 °C.
In a small bowl, add in and mix all the ingredients using your hands or with an electric mixer until a non-sticky dough is form.
Dust all-purpose flour over a small separate bowl and transfer the dough into the bowl.
Cover the bowl with a suitable lid or plastic bag to prevent the dough from drying. Keep the bowl in a warm place (about 21 °C - 26 °C) for it to rise.
After 2 - 8 hours, if the bread has increased in size (does not have to be double), stretch and fold all sides of the dough with your hands. Use some all-purpose flour to ease the folding, if the bread dough is too sticky.
After which, repeat step 3. Once the sourdough bread rises for the second time after another 2 - 8 hours, repeat steps 4 and 3 once.
When the dough rises for the third time after 2 - 6 hours, it should at least double in size. Spread a little flour onto your working space and transfer your sourdough bread from the bowl to your working top using a dough scraper.
In order to retain the air in the bread, please do not knead the dough. Gently form the dough into a round shape. Use flour as necessary to easy the process.
Place a kitchen towel in the small bowl and distribute a little flour all over the towel to prevent the dough from sticking to the towel. For one last time, repeat step 3 for another 1 - 2 hours.
Preheat baking oven and cast iron pot with a lid to 250 °C. Once the oven is hot enough, take the pot out. Be careful, it is extremely hot! If you do not own a cast iron pot with a lid, then please refer to this post for an alternative baking method (from step 9 onwards). Remove the cover of the pot and transfer the bread dough into your pot. Use a knife to score the surface of the bread and spread a little flour over the surface of the bread for a rustic look.
Cover the pot with a lid (be careful, it is very hot!) and place everything into the preheated oven. Lower the heat to 230 °C and bake for about 18 minutes.
After 18 minutes, remove the lid of the cast iron pot and continue baking the sourdough raisin bread for about 7 minutes or until the bread turn brown/ crispy. It depends on your baking oven, you might need to adjust the baking time accordingly. Just have fun and try it out.
After baking, remove the sourdough bread from the pot and place it on a cooling tray until it is completely cool down. Thereafter, you can store it in a cloth bag. Serve this sourdough plain or with some homemade baby fruit jam for breakfast. Finish it within 3-4 days.