Gather your tools. If you oven takes time to warm up, put it on now at 220C.
Weigh the flour to your mixing bowl add the salt and mix briefly.
Cut the margarine into cubes (around 1 cm/1/2 " is fine) and add to the flour. Then rub the margarine into the flour, until you get the mix to the consistency of breadcrumbs.
I like to use a Pastry Blender to get 80% of the way there.
After it is mostly incorporated you can either rub it in using just you finger tips, or if you are a cold handed (but obviously warm-hearted individual) you can rub it together between your palms.
Stir in the sugar to mix evenly
Add the eggs, milk (of your choice) and Sourdough starter to the mix and stir together to form a sticky dough.
Try to work the mixture as little as possible as overworking the dough will result in less fluffy scones. Don't worry too much, it will still result in scones which taste better than any shop bought variety.