Mix yeast with warm water and sugar in a small bowl. Cover with cling wrap, leave for 10 minutes until foamy.
Egg and Milk: Whisk milk and egg together.
Flour: Sift flour and salt into a separate bowl.
Add wet ingredients: Make a well in the flour, add yeast mixture, and butter and egg mixture. Mix together with a spatula. Once the flour is mostly incorporated, switch to your hands and bring it together into a ball. No kneading is required.
Proof 1: Cover the bowl with cling-wrap, then leave in a warm place for 1 – 1.5 hrs until it doubles in size.
Cut into 6 pieces: Place the dough on a lightly floured surface. Cut into 6 equal pieces, then shape into balls into spheres with a smooth surface by stretching the surface and tucking it under
Proof 2: Place balls on a lightly-floured tray or plate. Sprinkle lightly with flour, cover loosely with a lightweight tea towel. Put in a warm place to rise for 15 minutes until it increases in size by about 50%.
Roll out: Place a round on a lightly-floured work surface, flatten with your hand. Roll out into 3 – 4mm / 0.12 – 0.16" thick rounds (about 16cm / 6.5" wide).
Heat skillet: Rub a cast iron skillet with a very light coat of oil using 1/2 tsp oil on a paper towl (unless already well seasoned). Set over high heat until you see wisps of smoke.
Cook naan: Place a naan dough in the skillet and cook for 1 to 1 1/2 minutes until the underside is deep golden / slightly charred – the surface should get bubbly. Flip then cook the other side for 1 minute until the bubbles become deep golden brown.
Cook remaining naan: Remove, set aside, and repeat with remaining naan, taking care to regulate the heat of the skillet so it doesn't get too hot.
Finishing: Brush freshly cooked naan with melted butter or ghee (or garlic butter) Sprinkle with Black Cumin and coriander. Serve hot!