Parmesan Hasselback Potato Casserole

1. Preheat oven to 375°F with rack on middle position. In a bowl, whisk together the melted butter, olive oil, and 1¼ tsp kosher salt + ½ tsp freshly ground black pepper. Brush bottom of a 9-inch baking dish with a bit of butter mixture; set the remaining mixture aside.
2. Slice potatoes thinly and evenly cross-wise (for fastest and most even results, use a mandolin to slice potatoes. A sharp knife will work, too.)
3. Arrange potato slices upright (vertically and somewhat tightly) in prepared dish. Wedge chopped onions and garlic throughout potatoes. Brush with butter mixture, reserving ¼ cup for later.
4. Bake 1 hour uncovered. Brush on the reserved ¼ cup butter mixture and continue baking another 30 minutes until top is lightly browned. If it starts browning too quickly, cover loosely with foil.
5. Sprinkle top with shredded parmesan cheese and green onions. Bake 5-10 minutes until cheese is golden and melted. If desired, sprinkle top with a light dusting of kosher salt and black pepper. Serve immediately.

Notes

This dish comes together quickly once the potatoes are sliced. A mandolin can get the job done in 5-10 minutes. Be sure to allow enough time to bake. Dish is best when served hot and fresh from oven. Feel free to experiment with your favorite garnishes…crumbled bacon, other cheeses, and other herbs. It will be delicious any way you make it!