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Preheat the oven to 350°. Butter a baking dish. Arrange the sweet potato slices in concentric circles in the dish.
In a bowl, combine the hot water with 1 tablespoon of the honey and the butter; swirl to melt the butter. Pour the liquid over the sweet potatoes. Cover with foil and bake for 40 minutes, or until the potatoes are tender.
Meanwhile, in a small skillet, toast the cumin and coriander seeds over moderate heat until fragrant, about 40 seconds; let cool. Transfer the seeds to a spice grinder and grind to a powder. Transfer the powder to a small bowl. Stir in the lemon juice, oil, garlic, ginger and the remaining 1 tablespoon of honey; season with salt and pepper. Pour the dressing over the potatoes and serve.