Make sure your butter is really cold and cut into small cubes or grated. You can pop it in the freezer to cool it faster if you need to.
Add flour and butter to a mixing bowl and rub the flour into the butter using your fingertips. The mixture should be crumbly, but still feel cold.
Add the baking powder, salt and herbs to the flour mixture and gently stir through with a spatula or spoon.
Now whisk the egg and sourdough starter together and then pour into the centre of the dry ingredients.
Gently bring the wet and dry ingredients together to form a dry dough (don't overwork it or your dumplings will be tough).
Using your fingers, form 12 small balls of dough (they don't have to be perfect and they might seem crumbly, that's perfectly ok).
If you are going to do the long ferment method, refer to notes below for instructions.
Make sure your soup is gently simmering (not boiling). Carefully drop the dumplings into the soup. They might sink at first - don't panic, they'll pop back up in a minute or two.
Pop the lid on the soup and leave to gently simmer for 10 to 12 minutes.
Serve your soup and dumplings!