Mix together flour, baking powder and salt. Stir in the yogurt till the dough is too stiff for a spoon, then knead it in the bowl till it holds together well, adding more flour if necessary. Turn it out on a floured surface and continue kneading for about 5 minutes till the dough feels smooth and elastic. Form the dough into a ball and put it in an oiled bowl, covered with a towel, to rest for an hour or longer. Take the dough out and cut it into 10 equal pieces. Form each into a ball and press the balls flat into round discs. Heat a large frying pan or griddle, either seasoned cast iron or a good non-stick finish. Heat your oven to about 500 and have the broiler on (this is how the original recipe states it - I know with my oven it's either 500 degree oven OR the broiler, but you get the idea. Take 1 piece of dough at a time and roll it out on a floured surface till it is about 8-10 inches across and less than 1/4 inch thick. Lay it on the hot griddle and cook it over a medium heat for 4-5 minutes (I don't think mine took that long). It will puff up in places or all over, and there will be some blackish-brown spots on the bottom. Slide a spatula under the naan and transfer it to the oven, directly onto the rack, for a minute or two, just till it finishes puffing up into a balloon and begins to color lightly on top. Remove naan from the oven and brush it lightly with melted butter if you like. Continue this way with all the dough, stacking the breads into a napkin-lined basket. Serve the breads hot, fresh from the oven, or let them cool and wrap them up. To reheat, wrap them in aluminum foil, in packets of 4 or 5 breads and put them in a 400 degree oven for 10-15 minutes.