Prepare the Sweet Potatoes: Preheat oven to 500 degrees Fahrenheit. Gently scrub the skin of the sweet potatoes. Slice them into one-inch rounds, discarding any end pieces narrower than one inch to avoid burning, then add to a bowl with melted butter, olive oil, and spices. Toss until evenly coated.
2 pounds sweet potatoes, 2 tablespoons unsalted butter, 2 tablespoons avocado, 1 ½ teaspoon fine sea salt, 1 teaspoon ground cinnamon, ¾ teaspoon garlic powder, ½ teaspoon smoked paprika, ½ teaspoon black pepper, ½ teaspoon onion powder, ¼ teaspoon ground nutmeg