In a large mixer bowl, combine 1 1/2 cups flour, yeast, sugar, baking soda, and salt. Add warm water, oil, and yogurt to flour mixture. Blend at low speed until moistened; beat 1 minute at medium speed. Switch to the dough hook and gradually mix in enough of the remaining flour to make a smooth dough. Knead for 5 minutes.
Place dough in lightly oiled bowl and turn to grease top. Cover; let rise until dough doubles, about 45 minutes.
Preheat oven to 400°F with a pizza stone on the center rack, for at least 30 minutes before baking naan so the pizza stone gets very hot. (See notes for baking in a cast iron skillet.)
Punch the dough down, and divide dough in to 6 pieces. Let it rest five minutes covered. Roll out each piece of dough in to a tear drop shape about 8 inches long and ¼-inch thick.
Cook naan two at a time, use a spray bottle to lightly mist each piece of dough with water and put it wet side down on the pizza stone. Cook for about 2 minutes until the bottom is lightly browned and starting to puff. Spray with additional water and flip the naan over and cook an additional 2 minutes.
Remove from the oven and brush lightly with melted butter.
Wrap naan in aluminum foil to keep them warm until ready to serve.