Preheat oven to 425°F (218°C). Line a baking sheet with parchment paper or lightly grease.
In a large bowl, whisk together flour, salt, and baking powder (if using).
Cut in cold butter or lard until the mixture resembles coarse crumbs with pea-sized pieces.
Stir in sourdough starter. Add milk a little at a time until a soft dough forms.
Cover and rest dough for 30–60 minutes at room temperature, or refrigerate overnight for deeper flavor.
Turn dough onto a lightly floured surface and gently pat into a 1-inch thick rectangle. Fold once or twice, then pat back down.
Cut biscuits straight down with a sharp cutter. Do not twist.
Place biscuits close together on the baking sheet.
Bake for 12–15 minutes, or until tall and golden brown.
Serve warm with butter, honey, or gravy.