Mexican crema, sour cream or crème fraîche, for serving
Position a rack in the bottom third of the oven and preheat to 425º. Place a rimmed baking sheet in the oven to heat while you prepare the potatoes.
Leave the peels on the sweet potatoes and slice them in half lengthwise, then slice each half lengthwise into 3 or 4 pieces. (If your sweet potatoes are extra long or misshapen, you may want to slice them in half crosswise, as well.) Place them in a very large bowl, and drizzle the olive oil over them.
In a small skillet, toast the cumin seeds over medium-low heat, shaking frequently (the pan, that is), until they smell fragrant, 30 seconds to 1 minute. Grind the cumin fairly finely in a mortar and pestle or in a spice grinder. Sprinkle the ground cumin, paprika, chipotle and sea salt over the sweet potatoes, and toss them with your hands to coat evenly. Carefully spread them on the preheated pan in a single layer with a cut side down (if there are some that overlap, that's ok; they'll decrease in size as they bake) and drizzle any extra spiced oil left in the bowl over them. Roast in the oven for 20 to 30 minutes, until the undersides are deeply golden. Remove the pan from the oven, flip the spears over, and continue roasting until the second side browns and the potatoes are soft, about 20 more minutes. Sprinkle with a few pinches of flaky salt.
Serve the sweet potatoes hot from the oven with a dollop of crema, sour cream orcrème fraîche, if desired. Extra taters, should you be so lucky, can be stored in the fridge and reheated in the oven or toaster oven.
Adapted from Martha Stewart.
I found dried, ground chipotle in the bulk section of our local co-op, but lacking that, you can substitute 1/4-1/2 teaspoon of cayenne or other spicy chile powder.
Nutritional values are based on one of four servings.