Mix the yeast and sugar in 1/4 cup hot milk and keep it till it froths well. Beat the curds, with the remaining milk and mix the baking soda in it. Add this to the flour along with the yeast, ghee, egg, salt to taste and kneed well. Keep it, till it rises and become double in bulk.
Knead the dough again and make 12 balls. Roll it out so that one end is flat and the other end pointed. Those who have the tandoor oven can bake in it.
Alternately, grease a tin arrange the nan on it. Brush the top with water or milk, sprinkle a few gingelly seeds on it, press, so that they stick, and bake in a very hot oven (450 to 500 degree) till it is cooked for 4 or 5 minutes.