Slice into thick rounds (about 1 inch) or cut in a large dice.
Bring a large pot of salted water to a boil.
Add the sweet potatoes and simmer until just tender. Don't overcook - it will take 10 - 15 minutes depending on the size of the sweet potatoes.
Remove from heat and immediately drain really well.
Gently transfer the sweet potatoes to a heavy, large skillet.
Add the brown sugar, Karo syrup, butter, and salt.
Place on medium heat until the butter and brown sugar melt and the mixture is thick and bubbly.
Reduce heat to low and simmer for about 1 ½ hours, basting every 10-15 minutes.
Just before serving top with the marshmallows and place in a 350°F oven for 10 minutes or until marshmallows get golden and melty.
Storage:You can keep leftover Southern candied yams covered in the refrigerator for three to five days. Put in an airtight container or cover with plastic wrap.The marshmallow topping doesn't freeze well. So, if you wanted to freeze the candied yams (for instance, when prepping the dish in advance) do so before topping with marshmallows. It'll last for up to three months. Just be sure to let them thaw in the fridge before topping and baking.Tips:
Fresh sweet potatoes are preferable in this recipe, as opposed to canned yams. Pre-softened sweet potatoes from a can have the potential to become too mushy and don't candy as well.
For the best candied yams, be sure to use dark brown sugar. It makes a deeper, more flavorful candied taste than white sugar.
Watch the marshmallows carefully in the oven. They'll toast rather quickly. We want a nice, gooey topping, rather than charred marshmallows—unless you prefer 'em that way!