This year I grew bulb onions for the first time. As an experiment I grew them a variety of different ways, but the ones that did the best were the ones that I started from seed indoors in February alongside my eggplant and celery. I felt like I was already on to something and then my suspicions were confirmed when I read @matt_mattus book, Mastering The Art of Vegetable Growing. The chapter on onions talks about the best way to grow them and you guessed it: start them from seed and then transplant the seedlings.
This is in part because they have a long growing season. I started these seeds in February and harvested the first onions in early September. I'm going all in on onions started from seed next year with a couple different varieties.
On my quest to grow a majority of the food that I eat onions interest me because they're pretty much the base of everything I cook and certain varieties have the potential for long term storage. This year I also made green onion powder (mentioned in a previous post) as a way to extend the shelf life of my not so shelf stable green onions..