Bloom the yeast. Add the warm water, granulated sugar, and active dry yeast to a large mixing bowl. Stir to combine, cover the bowl with a clean kitchen towel, and let the mixture rest for 5–10 minutes, or until the yeast looks foamy.
Mix the dough. Add the bread flour, salt, sourdough discard, Greek yogurt, and olive oil to the yeast mixture. Mix until the ingredients come together into a shaggy dough.
Knead the dough. Transfer the dough to a lightly floured work surface. Knead by hand for about 5 minutes, or until the dough is smooth and elastic. Add only a small amount of additional flour as needed to keep the dough from sticking.
Let the dough rise. Place the dough in a lightly greased bowl and cover it with a clean kitchen towel. Let it rise in a warm place for 1–1½ hours, or until noticeably puffy and approximately doubled in size.
Divide the dough. Turn the dough onto a lightly floured surface and divide it into 8 equal portions. Shape each portion into a smooth ball.
Rest the dough balls. Cover the dough balls with a clean kitchen towel and let them rest for 10–15 minutes. While they rest, preheat a cast-iron skillet over medium-high heat.
Make the garlic butter. In a small bowl, combine the melted butter, garlic salt, and finely chopped parsley or cilantro. Set aside.
Roll out the naan. Working with one dough ball at a time, roll it into a round or oval approximately 6–7 inches in diameter. The naan does not need to be perfectly shaped.
Cook the naan. Place the rolled dough in the hot, dry cast-iron skillet. Cook for 1–2 minutes, or until bubbles form and the underside develops golden-brown spots. Flip and cook the other side for another 1–2 minutes. Adjust the heat as needed to prevent burning.
Brush with garlic butter. Remove the naan from the skillet and immediately brush the top with the prepared garlic butter. Repeat with the remaining dough, keeping the cooked naan covered with a clean kitchen towel so it stays warm and soft.
Serve. Serve the naan immediately while it is warm and tender.