Preheat oven to 400 degrees Fahrenheit. Peel the sweet potatoes. Then, using a mandolin or a sharp knife, thinly slice the potatoes into rounds, about 1/8 inch thick.

Generously butter a gratin dish, or a casserole dish (about 9×13). Sprinkle the bottom with a couple of tablespoons of grated Parmesan cheese. Place one layer of potatoes (use 1/3 of the potato slices) in the prepared dish, overlapping slightly as you layer them. Sprinkle with 1/4 teaspoon salt and a few grinds of black pepper.

In a medium saucepan, combine the heavy cream, chopped sage and rosemary, minced garlic, nutmeg, and a generous pinch of salt. Bring the cream mixture to a low boil over medium heat, then reduce heat to low and maintain a simmer. Simmer for about 10 minutes, or until the mixture has reduced by 1/4.

Add the eggs to a medium bowl and whisk until lightly beaten. Slowly pour the hot cream mixture, while whisking continuously, into the eggs.

Pour 1/3 of the cream and egg mixture over the first layer of potatoes in the prepared dish (about 2/3 cup). Sprinkle with 1/3 cup of Parmesan cheese, then add the next layer of potato slices and repeat twice (three total layers of potatoes).

After adding the final layer of cream and cheese, cover the baking dish with foil. Bake covered for 40 minutes, or until the potatoes are tender.

While the potatoes are baking, combine the Panko Bread Crumbs, remaining Parmesan cheese, Paprika, Garlic Powder, Onion Powder, pinch of Cayenne, and olive oil in a medium bowl.

After the potatoes have been baked for 40 minutes, remove the foil. Carefully spread the breadcrumb mixture over the top of the potatoes and return to the oven. Bake uncovered for an additional 20 to 25 minutes, or until the bread crumbs are browned and the mixture is bubbling. Cool slightly before serving.