Sweet potatoes typically pair with cinnamon, nutmeg and clove. So the Indian spice mix called garam masala (‘warm spices’), which uses these plus a few others (usually cardamom, black pepper and cumin), is a logical next step. —zora
Peel sweet potatoes and slice into 1-inch-thick rounds. Lay out on baking sheet and drizzle with vegetable oil and sprinkle with salt. Place in oven and roast until browned and soft, about 30 minutes.
While the sweet potatoes are roasting, slice the onion into thin half-rings and peel and grate the ginger.
Heat the ghee in a heavy skillet over medium heat. Add the onions and the ginger paste (the ghee will spatter—stand back) and cook, stirring occasionally, until the onions are soft and translucent, not browned.
When the onions are tender, either remove the onion-ginger mix from the pan or push it off to one side. Turn the heat up to high and add the chilis. Stir and fry until just darkened, about 5 seconds. Add the cumin and coriander seeds. Stir and fry just until fragrant, about 5 seconds. Remove the pan from the heat and stir in the garam masala.
When the sweet potatoes are finished roasting, place them in a shallow serving dish. Drizzle the ghee with the onions and spices over the potatoes, garnishing with the red chilis (they're not really meant to be eaten). Serve promptly, before the ghee cools.
Notes: The exact proportions and ingredients of garam masala vary; if you can get a freshly ground mix from a good source, use it. But you can also make your own--I like 1 teaspoon each cardamom, cumin, cloves and black pepper, plus a stick of cinnamon and about half a nutmeg. For ghee, you can also buy this premade, or you can make your own by simmering a pound of butter in a heavy saucepan for about an hour, then straining out the solids. Stored in a clean jar in the fridge, it lasts several months.