This is such a classic side dish for Thanksgiving and Christmas.  I know many people who have variations of this recipe handed down through the generations.  Years ago, I tasted this dish - can't remember where, and I neglected to get a recipe, so when I made it, I did so based on the memory of what it tasted like.  We have been having it ever since.
4 large yams, peeled and cut into equal sized 2 1/2 inch chunks
10 garlic cloves, skin on
3 Tblsp. finely grated fresh ginger
3 Tblsp. Olive oil
pinch of Allspice
1 Tblsp. pure Maple Syrup (or honey)
salt and pepper
Parmesan Cheese
butter
juice and zest of 1 lemon

Preheat the oven to 350 degrees.   Put the cut yams and garlic cloves into a casserole or baking dish.  In a bowl, mix up the lemon Ginger, Allspice, Maple Syrup and Olive Oil.  Pour this mixture onto the yams and garlic, stirring to evenly coat.  Season with Salt and Pepper, then add 4 or 5 knobs of butter through out the dish.
Bake for 45 minutes, half way through, use a flipper to turn the yams and garlic.
When finished roasting, squeeze out the garlic from the skins, mash the yams and garlic together with a potato masher, and add in about 1/2 a cup of Parmesan cheese, stirring to mix through.  Also, adjust for salt and pepper, and add in a few more knobs of butter. This dish can be made the day before, and reheated the next day in a covered casserole dish.