Proof your yeast by mixing the warm water, sugar, and yeast in a small bowl or mixing cup. Cover and set aside for 10 minutes and it should foam up.
Whisk the egg, take what you need, then whisk the milk into the egg.
Sift together the flour and salt in your mixing bowl.
Add the yeast mix, melted butter, and egg mix to the flour. Mix to combine using your spatula. Once you have a mostly-combined dough, work it a bit with your hands to fully mix. You don't need to full-on knead it, but it won't hurt if you do a bit of kneading to mix.
Form the dough into a ball, put it back in your mixing bowl, and cover it with a tea towel. Let it rise for about 1-2 hours.
On a lightly floured surface, cut the dough ball into six pieces. Roll each piece into a ball. Place the balls on a flat surface or baking sheet, cover with your towel, and let rise again, for about 15-30 minutes.
Using a rolling pin, roll each dough ball out flat. You're aiming for about 3-5mm thick.
Heat your cast iron skillet over high heat, until it's starting to lightly smoke. To cook the naan, place one flat dough on the skillet and cook for about 1-1.5 minutes. Then, flip it and cook the other side for about 1 minute.
Serve warm and enjoy!