Pre-heat oven to 425F. Line a baking sheet with parchment, or grease it well.
Combine the 1 cup flour, 2 tsp baking powder, and 3/4 tsp salt.
Cut the 1/2 cup cold butter into small cubes, and gently start to pinch the butter into the flour mixture with your finger tips, till it resembles coarse bread crumbs.
Add the starter into your flour and butter mixture and give it a gentle mix with a spatula or your hands. It might take a bit of effort to mix it, in but it will get there.
Once the dough has been combined, and is starting to form into a ball, flour your counter and pat the dough out into a large rectangle, about 12" x 6". It should be about half an inch thick.
Using a butter knife, cut the dough into 8 squares (about 3" x 3" each).
Place the biscuits onto the baking sheet, making sure they are about an inch apart, they will spread a bit as they bake.
Bake for 20 - 23 minutes.
Once out of the oven, you can server warm, or cool and freeze to eat later. They will keep well in the fridge for about three days.