Sweet Potato Parsnip Gratin

1. Preheat oven to 400 degrees Fahrenheit. Grease a small casserole dish. Combine parsnips and potatoes in a medium mixing bowl and set aside. In a small bowl, whip the garlic and 1 tablespoon + 1 teaspoon margarine together.
2. Add the coconut oil, sage, nutmeg, and 1/4 to 1/2 cup milk. to margarine. Heat mixture over low heat or microwave until just melted, 10 to 20 seconds. Slowly add another 1 cup milk to the mix and a generous pinch salt. Season with pepper, to taste. Whisk together and pour over vegetables.
3. To layer vegetables, alternate parsnip and sweet potato slices in prepared casserole until bottom is covered. Top with 1/2 the leeks. Place another layer on top, alternating between parsnips and sweet potatoes.
4. Top with remaining leeks and pour milk mixture over vegetables, using any leftover milk, if needed (milk mixture should come up to within a 1/2" from the top of the dish). Cover and bake 35 minutes.
5. While the vegetables bake, heat remaining margarine in a small pan and sauté bread crumbs over medium heat until brown, about 5 minutes. Remove cover from casserole and bake another 10 minutes, uncovered until the top starts to brown and vegetables caramelize. When vegetables are golden and tender, top with prepared bread crumbs and bake an additional 5 minutes to let bread crumbs absorb into some of the liquid.
Source of recipe: I had never made anything au gratin before because of all the cream and cheese in every recipe, but I was craving a potato dish. I made one up using ingredients that are a little more exciting than just plain old potatoes.