Add the warm water (100°F / 38°C) to a large mixing bowl. Sprinkle the instant yeast over the water and let it sit for about 1 minute until it looks slightly cloudy.
Add the sourdough discard, yogurt, milk, olive oil, sugar, and salt. Stir until the discard is fully dissolved and the mixture is smooth and uniform.
Add the flour 1 cup at a time, stirring with a wooden spoon. Once too thick to stir, use your hands to bring it together. Knead for 2 to 3 minutes until smooth and elastic.
Drizzle a little olive oil over the dough and turn to coat. Cover the bowl tightly and let rest at room temperature for 30 to 60 minutes until puffed and roughly doubled in size.
Turn the dough onto a lightly floured surface and gently press out any large bubbles. Divide into 8 equal portions and roll each into a smooth ball. Cover and rest for 10 minutes.
Working with one dough ball at a time, roll it out into an oval or teardrop shape about ¼ inch (6mm) thick. Keep the other balls covered.
Preheat your cast-iron skillet over medium-high to high heat for 2 to 3 minutes until very hot. Do not add any oil to the pan.
Lay one rolled-out naan into the hot dry skillet. Cook for 1 to 2 minutes until bubbles form and the underside is golden, then flip and cook for 1 to 2 minutes more until puffed and spotted. Remove from pan.
Combine the melted butter with minced garlic. Brush each cooked naan generously with garlic butter while still hot. Sprinkle with parsley or cilantro and flaky sea salt if desired.
Stack the finished naans on a plate and cover loosely with foil to keep warm. Serve immediately warm, or use as a wrap, pizza base, or alongside curries and dips.