I need to substitute fresh yams for canned, but I want the sweetness I have always used Bruce's canned Yams for My Sweet Potato Casserole.  Unfortunately, this year with the pandemic, I cannot find any available. I still want to make the casserole and want it to taste the same. I know to boil the yams, but what else do I need to do in order to get that sweet taste?
If you want to devote the time to get the maximum sweetness, you can take advantage of natural enzymes to accomplish your goal.  If you can  hold your yams between 135 and 170°F (57 and 77°C) for a couple of hours, you can dramatically increase the sweetness. They will still be hard at this point, so will need roasting to soften. A sous vide device will be the best way to do this, but you can do a decent job of improving sweetness by roasting, wrapped in foil, in a 300 F (149 C) oven for about 2 hours.  The science and process is explained in detail here.