Feed your sourdough starter 6-8 hours before you plan on making the dough (very dependent on how active your starter is).
Mix all of the dough ingredients (starter, flour, milk, yogurt, salt) in a bowl and gently knead with your hand for 2-3 minutes until smooth. You may need to add a little extra flour of milk depending on the consistency of your starter. The dough should form into a smooth ball but still be slightly sticky.
Cover the dough and let rise in a warm place until it has almost doubled in size. For me, this typically takes 5 hours at room temperature but can vary anywhere from 3-8 hours based on the temperature/starter ripeness. You can also mix the dough and then let it rise in the fridge overnight (for up to 48 hours).
Scrape the dough out onto a lightly floured counter top. If you are adding toppings, lightly knead them into the dough until just combined.
Divide the dough into 12 even pieces (about 85g each) and roll each piece into a small ball. Cover the dough balls and let rest for 10 minutes.
While the dough is resting, prepare the garlic butter. In a small sauce pan melt the butter over low heat and add in the garlic and cilantro. Cook for about 5 minutes or until the garlic is soft and no longer bitter.
Heat your cast iron skillet (10 inches or larger is ideal) over medium to medium-high heat and lightly brush with olive oil.
Roll out your first ball to a little less than ¼ inch thick.
Cook each naan for 1-2 minutes on each side. Flip when the top of dough starts to bubble and puff up. You're aiming for those classic brown spots so adjust your heat accordingly.
Roll out your next naan while one is cooking.
Place the cooked naan on a cooling rack and brush with garlic butter.
The naan is best served warm but will keep in the fridge for up to 3 days.
Notes
To reheat: place naan on a baking sheet in the oven at 450°F until warm (about 2-3 minutes) or reheat in the cast iron skillet!