A pro who knows weighs in on onion slice-ery:
I read the piece on cutting onions, and as far as being more or less oniony, the less times you cut the onion (and the sharper your blade is), the less damage you’ll do the cell structure, resulting in less of the sulfuric compounds mixing and producing the tear-inducing sulfuric acid. A dull knife (or food processor blade) rips and crushes lots of cells, resulting in more sulfur, more sulfuric acid, more tears, and a stronger onion flavor.
For those reasons, your method is right on the money. It doesn’t result in the wierd, oddly-shaped pieces that come from the first cuts on the sides, the large, flat pieces that stand out and don’t cook at the same rate as the rest. If you’re trying to cook them evenly and deeply, like for your onion tart, you want to have them as close to identical as possible, as you well know. For diced onions, leave the root end intact, and make radial cuts almost to the root end, then turn the onion 90 degrees and cut across for wonderfully even diced onion. Having said that, cutting across the onion (making half-rings) will result in a completely uniform thickness for each slice of onion, instead of pieces with tapered ends and thick centers. It may not make much difference, but as long as I’m nitpicking, I figure I’d mention it.
Finally, the green sprouty thing in the middle is the onion shoot (the part that would break the surface and eventually become an onion blossom if given more time underground) and is a sign that your onion is old or may not have been stored properly. It’s not the end of the world, obviously, just something that you’d like to avoid, given the opportunity.