In a large bowl, combine flour, salt, and sugar.
Grate frozen butter into the dry ingredients with a cheese grater and cut in with a pastry cutter. (You can also use your hands or a food processor).
In a separate bowl, combine the sourdough starter and cream. Add the mixture to the flour mixture and mix until combined, being careful not to over mix. Cover with a towel and allow to ferment at room temperature for 8-12 hours.
Sprinkle over baking powder, add egg, and any add-ins you would like. Knead together until just combined.
On a clean, lightly floured surface, roll the dough out into a circle about 8” in diameter. Cut the circle into 8 equal parts.
Place on a prepared baking sheet lined with parchment paper about 2” apart.
Put in the fridge for 30 minutes, preheat the oven to 400°.
Brush the top of the scones with cream and sprinkle with sugar.
Bake for 20-25 minutes or until golden brown.
