Mix warm water, sugar, and yeast together in small bowl. Let sit until foamy, about 10 minutes.
Place flour in large bowl or on flat surface. Stir in yeast mixture, yogurt, salt, and oil.
When the mixture holds together, place on flat surface and knead until smooth and shiny, about 10 minutes.
Cover and let rise in warm place until doubled in size, about 1 hour.
Divide dough into 8 equal portions.
Heat cast iron pan over high heat. Lightly grease surface with oil to prevent dough from sticking.
Roll out portion of dough into an 8-inch circle.
Place dough in pan. When it puffs and bubbles and burnt spot appear, flip it over and cook the other side.
Repeat until all portions are used.
If using butter, brush naan with melted butter.
Serve.