No, not stupid at all!Stupid question...I've never planted these before but did this time and they are already a foot tall! But does it produce one onion per plant? Or more per plant? Above ground or below ground...like I said stupid question.
Yes, 1 onion per plant. Onions from seed can take a long time to grow, so planting an onion set (a "baby" onion, really) means they can grow and make a decent sized bulb in less time. An onion is actually made up of specialized leaves below ground.
Usually you don't use a lot of nitrogen fertilizer on root crops, but because the "root" is really modified leaves, that rule doesn't apply with onions.