Preheat oven to 450 F (230C) and line a baking sheet with foil.
Spread your sweet potato chunks in a single layer on the baking sheet, then drizzle on the oil and season with salt and pepper, and optional cayenne (see note). Toss gently with your hands to coat each piece in oil.
Roast the sweet potatoes for about 40 minutes or until soft. Stab one with a fork to test it.
While the sweet potatoes are roasting, lightly toast the pecans by heating them in a dry skillet over medium heat until they start to smell toasty.
In a small saucepan over low heat, heat butter, maple syrup, and cayenne. You can let it bubble for a few minutes if you want to thicken it up a bit, but don't let the butter burn.
After you remove the pan from the oven, carefully transfer the sweet potatoes to your serving dish. Sprinkle over the nuts and pour on the maple butter mixture. Toss lightly.
