In a small bowl, add in all the ingredients according to the list. Mix the ingredients either using hands or an electric mixer until a sticky dough is form. If you are using an electric mixer, mix the ingredients at the lowest level for about 3-5 minutes until you get a sticky dough. You can find the rye sourdough starter recipe here. Cut out a suitable piece of a parchment paper and place it into the baking dish or the loaf tin.
Transfer the sticky rye bread dough evenly into the dish or loaf tin. Moist a spoon/knife with water and smooth out the surface of the bread dough.
Dust a little all-purpose flour over the top of the sourdough.
Cover the baking dish or tin with a small plastic bag to prevent the dough from drying. Make sure that the bag is higher than the dish/tin, so that the dough does not stick to the plastic bag. Thereafter, keep the bowl in a warm place (about 21 °C - 26 °C). The sourdough will work faster in a warmer place.
Wait for 12 - 24 hours, the rye bread dough should double in size. The dough should be at least of the same height of the baking dish/ loaf tin. If the dough reaches its maximum height and starts to fall, then you should definitely bake the rye sourdough sandwich loaf.
Preheat baking oven to 230 °C.
Reduce the heat to 200 °C. Place an extra baking tray upside down into the highest level of the baking tray and bake the rye sourdough for a total of 25 - 30 minutes. It depends on your baking oven, you might need to adjust the baking time accordingly. Just have fun and try it out.
Depending on your preference on how “brown” you want your baby rye sourdough to be, remove the top baking tray after 20 - 25 minutes (be careful, it is very hot!).
After baking, remove the sourdough bread along with the parchment paper from the baking tray/tin and place it on a cooling tray until it is completely cool down. Thereafter, remove the parchment paper gently. 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.