Prepare the Dough: In a large mixing bowl, combine the active sourdough starter, flour, yogurt, milk, olive oil, salt, and garlic powder.. Mix until all the ingredients are well combined. If the dough feels too dry, add water a little at a time until the dough comes together. The dough should be more on the firm side, so resist adding too much water. Just enough until it comes together.
Knead the Dough: Turn the dough out onto your work surface and knead for about 5-7 minutes until smooth and elastic. Place the dough back in the bowl, cover with a damp cloth, and let it rest for 4-8 hours at room temperature or until it has doubled in size. The resting time will vary greatly depending on factors like room temperature and strength of starter.
Shape the Naan: Divide the sourdough naan dough into 6-8 equal pieces and shape each portion into a ball. Using a rolling pin, roll out each piece of dough on a lightly floured surface to about ¼ inch thickness.
Cook the Naan: Heat a cast iron skillet or non-stick pan over medium-high heat. Place one rolled-out dough ball on the hot skillet and cook until bubbles form on the surface, about 1-2 minutes. Flip the naan and cook the second side until golden brown spots appear, about 2-3 minutes more. Repeat with the remaining dough balls.
Finish and Serve: Using a pastry brush, brush the cooked naan with melted butter or ghee while still warm. Sprinkle with fresh herbs or minced garlic if desired.