Add wet ingredients to a big glass jar or medium- sized bowl and stir with a wooden spoon until the starter has completely dissolved in the liquid.
Incorporate about 1/4 cup of rye flour at a time into the mix while stirring continuously.
Cover the top tightly and allow to ferment for 8-12 hours. A glass container works best because you can check the activity of the sourdough.(You want it to be very bubbly).Never use any metal objects to stir or store fermenting cultures.
Mix egg, sugar and salt and stir until the sugar has dissolved.
Add mixture to the batter and stir well.
Whisk in the baking soda and allow to rest for another 5 minutes, it will help the batter to rise and to tone down the tangy flavour.
Depending on the consistency of your rye sourdough starter you might have to add a little water to achieve the typical runniness of pancake batter.
Pour the batter into a pan at medium heat and cook until the top of the pancake starts to form a film. Flip the pancake and cook until golden brown.