In a large bowl, whisk together the sourdough starter, warm milk, yogurt, and 2 tbsp oil until smooth. Add flour, sugar, salt, and baking powder if using. Stir until a shaggy dough forms, then knead on a floured surface for 2 to 3 minutes until smooth and slightly tacky.

Place dough in a greased bowl, cover, and let rise at room temperature until doubled, about 1 ½ to 2 hours.

Turn dough out, press out air, and divide into 6 equal pieces. Roll each into a ball, place on a floured surface, cover, and let rest 15 minutes.

Heat a cast‑iron or heavy skillet over medium‑high heat until smoking. Roll one ball into a ¼‑inch‑thick oval. Cook in the dry skillet 1 to 2 minutes per side until bubbly and charred in spots. Repeat with remaining dough, adjusting heat as needed.

Brush each hot naan with melted butter or garlic butter and sprinkle with nigella seeds or herbs. Stack and serve immediately.