Combine yeast, water, and 1 tsp sugar in a small bowl. Set aside until frothy, 4-5 minutes. Sift flour, salt, remaining 1 tsp sugar, and baking powder into a large bowl.
Once the yeast has bloomed, add the yogurt, Easy Onion, olive oil, dried onion, and fennel seeds. Stir to combine. Pour the yogurt mixture into the dry ingredients and gently mix with a fork until combined. Using your hands, combine until mixture transforms from a sticky batter into a soft, pliable dough. Place the dough onto a parchment lined baking sheet and cover with plastic. Let dough rest in a warm for 2-4 hours.
Remove dough from the baking sheet and separate into 6 equal portions. Lightly roll each portion in flour to keep from sticking together. Roll each piece of dough with a rolling pin into a teardrop shape, 8 to 9-inches long, and 4-inches wide at its widest point and ¼-inch thick. Once formed, pick up the dough by the narrow end and wiggle it. Repeat this method with the remaining dough.
Place a large, dry, cast-iron skillet or sauté pan with a lid, over high heat until smoking.
Wet your hands with water and pick up naan. Flip-flop the dough from one hand to the other to lightly dampen it. Gently lay it in the skillet, pour in 2 Tbsp of water and quickly place a lid on top. Cook until the dough begins to bubble, 1-2 minute. Flip the naan over and repeat. It should be blistered and toasted.
Remove the naan from the skillet, brush lightly with butter and sprinkle with sea salt. Transfer to a towel-lined plate, repeat with the remaining dough.