Grate cold butter into a bowl and combine with flour as described above. Mix in the sourdough starter discard, buttermilk, and sugar, then stir until fully combined. Cover the bowl and leave it at room temperature to ferment for 10-12 hours. Before shaping, mix the salt, baking powder, and baking soda in a small bowl, breaking up any lumps. Gradually incorporate this mixture into the fermented dough, ensuring even distribution.