How to Make It
In glass measuring cup, combine yeast, sugar, and water and let sit for 10 minutes. In the meantime, mix flour, baking soda, and baking powder in large bowl.
Whisk together the yeast mixture, yogurt, and milk and stir into dry ingredients. Knead with your hands until the dough forms a smooth, soft ball, about 2 minutes. Place dough in an oiled bowl and cover with plastic wrap. Leave at room temperature until doubled in size, about 2 hours.
In large sauté pan, sautée onion, cumin seeds, and cardamom over moderate heat for 10 minutes, stirring every minute, until reduced and golden brown.
Remove dough from bowl and turn onto a well-floured surface. Knead briefly and divide dough into 12 equal portions. Roll into 1/4 inch thick ovals, approximately 6 inches wide.
Heat a cast-iron skillet over moderately high heat. Sprinkle each portion with poppy seeds and press them into the dough. Brush the dough with melted butter and place in a skillet. Cook for about one minute, until the dough puffs up. Flip the bread, cover the pan, and cook for one more minute. Remove from the pan and brush both sides with butter and sprinkle with salt.
Preheat the broiler. Place naan on a baking sheet and top with caramelized onion. Broil in the oven for 2 minutes, until naan turns golden brown around the edges.