First of all, take 2/3 cup of warm water and add yeast and sugar to it. Mix it with spoon and keep it aside for 10 minutes so that yeast rises.
Now shift together all purpose flour, whole wheat flour and baking powder. Add salt and yogurt to it and knead this to a soft dough with the help of that risen yeast water.
Now take Oil in your hand and again knead the dough so that its smooth. Transfer this dough into a oil greased bowl and cover the bowl with cling film. keep the bowl aside for 45-60 minutes. After 45 minutes it would be almost double in size.
Now take out the dough and knead again for 45 seconds so that extra air releases. Divide this dough into 10 equal parts.
Keep tawa on medium-high heat and sprinkle some flour onto the worktop / rolling board and also dust the dough balls with some flour. Roll the ball into a circle of 4-5 inch diameter with medium thickness. (Its not necessary that the circle will come in true circle shape owing to stretchy nature of dough. Naan are known to be not in circle.)
Sprinkle some kalonji and again roll it so that the seeds get sticked to the surface, now flip the Naan and pat it with little drops of water all over this side. We do this step so that Naan bubbles properly and gets an evenly brown base.
Place the Naan with seeded side up on the heated tawa. When you see Naan getting bubbled on top side, turn your tawa to face the flame and move it in slow circular motion so that you get brown spots evenly on the Naan.
Now with the help of tongs / Steel spatula scrap the naan off from tawa. If you like little more brown Naan then cook it on direct fire for a minute regularly flipping the sides.
Place the hot naan in a casserole and spread some butter on top. Make rest of the Naan similarly.