Peel the sweet potatoes and slice into 1/2-inch rounds. Coat a 9×13-inch ceramic baking dish with cooking spray (avoid metal pans; they can add a slight metallic flavor). Add the potato slices, sprinkle with salt, and toss to coat.
Preheat the oven to 375°F.
In a medium pot over medium heat, add the butter, brown sugar, maple syrup, cinnamon, nutmeg, ginger, and cloves. Cook, whisking occasionally, until the butter melts. Stop stirring and bring to a gentle boil. Boil for 2 minutes without stirring.
Remove from heat. Stir in the vanilla. Zest the clementines to get 1/2 teaspoon zest, then juice them to get 2 tablespoons juice. Add both to the sauce and mix.
Pour the warm sauce over the potatoes. Gently toss to coat as evenly as possible.
Bake uncovered for 20 minutes. Remove from the oven, stir the potatoes, cover with foil, and return to the oven for another 20 minutes. Remove, stir again, recover with foil, and bake 20 more minutes or until the potatoes are fully tender.
Remove from the oven. The sauce will look thin, but thickens as it cools. Taste and add a pinch more salt (I usually add another 1/4 tsp) if needed. Enjoy warm.
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Notes
Storage: Cover and refrigerate for 3-5 days. The sauce thickens when chilled but loosens as it warms. Reheat in the microwave.Make ahead: Peel and slice the sweet potatoes up to 1 day ahead; store in an airtight bag in the refrigerator. The sauce can also be made ahead. Store it in an airtight container in the fridge and rewarm on the stovetop or in the microwave before using.