As a baking site, I will always say homemade puff pastry is better than store-bought. But it's also ok to use store-bought too! Different brands come in various quantities, so you may have more or fewer tarts depending on your brand and your size cutter. But the spirit of the recipe is the same no matter what.
If you don't want to make the caramelized onions, this ingredient can be skipped.
The size of the puff pastry bites can vary, depending on the quantities you wish to bake up. If you want more, use a smaller cutter. During testing, I made as few as 12, and as many as 24 in a single recipe by using a smaller cutter. The baking time will vary slightly, though not by a lot.
These bites are best eaten on the day they are made. Leftovers can be stored in an airtight container in the fridge or freezer and reheated in a toaster oven.
The total time to make this recipe depends on whether or not you make your own puff pastry, so keep that in mind.
Putting the jam in the piping bag isn't strictly necessary, but it makes quick work of adding the jam to the center of the pastry. This is useful since it should be done as quickly as possible to minimize the time the partially baked pastry spends out of the oven. If you don't have a piping bag, use a Ziploc bag with a square corner, then snip off the corner, and, voila, a make-shift piping bag.