Peel and dice the potatoes.
Preheat the oven to 350 degrees F.
Grease a large casserole dish and fill with the cubed sweet potatoes.
In a medium sauce pan, melt butter, syrup, sugar, orange juice, and spices together.
Bring to a boil over medium high heat.
Keep at a rolling boil, whisking constantly, until the sauce begins to caramelize. You will start to see it thicken and come away on a whisk or spoon. This can take up to 10 minutes. Remove from heat. Stir in the vanilla and zest.
Pour the caramel mixture over the potatoes. Stir to coat all of the potato pieces.
Bake for 30 minutes, stir, then bake for an additional 30 minutes, or until the sweet potatoes are fork tender.
Remove from the oven. The sauce will thicken as it cools.
Serve with your favorite holiday dishes.