Preheat oven to 400 degrees F.
In your mixer, combine the butter, sugar, salt and flour until the mixture resembles coarse crumbs.
Add in the sourdough starter, baking powder and baking soda and mix just until combined. The dough will come together with just a few crumbs in the bottom of the mixer bowl.
Turn out the dough onto a well-floured surface.. pat with your hands 1/2" thick (shape doesn't matter). Fold the dough into thirds like you would a letter to create a rough triangle. Pat the dough to 1/2" again, and repeat the folding process. Pat the dough out for the third time to 1" thickness and the fold like a letter again.
Using a biscuit cutter or floured glass, cut or punch out as many biscuits as you can do. Do not twist as you cut. Transfer to a parchment lined baking sheet 1-2" apart. Gather the scraps, fold into thirds about 1" thick, then cut out more biscuits.
Bake the biscuits at 400 degrees for 12-15 minutes or until light brown.