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White and Sweet Potato Gratin

David Scott Allen, Cocoa & Lavender
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Ingredients
  

  • 2 large russet potatoes about 2 pounds
  • 2 large sweet potatoes about 2 pounds
  • kosher salt
  • freshly ground pepper
  • 6 teaspoons chopped fresh rosemary more as desired
  • nutmeg as needed
  • 1 1/2 cups heavy cream
  • 6 ounces grated Gruyère cheese
  • 1 1/2 ounces grated Parmigiano-Reggiano

Instructions
 

Oven Version

  • Preheat oven to 400°F.
  • Peel and thinly slice all four potatoes, keeping separated by color.
  • In a 10-inch round (or similar-sized) deep casserole, place half the white potatoes on the bottom in a thin layer, overlapping slightly. Sprinkle with salt, pepper, 1 1/2 teaspoons chopped rosemary, and a grating of nutmeg.
  • Next, cover with a layer of half the sweet potatoes; sprinkle with salt, pepper, 1 teaspoon chopped rosemary, and a grating of nutmeg.
  • Repeat layering using up all remaining potatoes, sprinkling each layer with salt, pepper and rosemary.
  • Pour cream over potatoes and cover casserole with lid (or foil). Bake for 1 hour to 1 hour 15 minutes (see notes).
  • Meanwhile, mix the grated cheeses. Remove the top and check the potatoes for doneness (if not tender, return to the oven for a bit). Sprinkle the cheese mixture evenly over the top, then return to the oven, uncovered, for 3 minutes, or until cheeses are nicely melted and bubbly.

Microwave Version

  • Peel and thinly slice all 4 potatoes, keeping separated by color.
  • In a deep 10 x 12 microwave safe casserole that has a cover, place half the white potatoes on the bottom in a thin layer, overlapping slightly. Sprinkle with salt, pepper, 1 1/2 teaspoon chopped rosemary, and a grating of nutmeg. Cover with a layer of half the sweet potatoes; sprinkle with salt, pepper and rosemary.
  • Repeat layering using up all remaining potatoes, sprinkling each layer with salt, pepper, 1 1/2 teaspoon chopped rosemary, and a grating of nutmeg.
  • Pour the cream evenly over the potatoes and cover casserole (I don't recommend using plastic wrap). Microwave on HIGH for 18 minutes.
  • Meanwhile, mix the grated cheeses. When the potatoes are done, remove the cover and sprinkle evenly with the cheese mixture. Microwave uncovered for 3 more minutes at HIGH power.

Notes

Serves 8.
• Baking and microwaving times will vary depending on your casserole and your oven/microwave. Test the potatoes with a fork or knife for doneness after 18 minutes. A little overdone is better than a little underdone.
• If making this in a smaller casserole (8-inch square, for example), make sure it is deep enough that it won't bubble over. There will be leftover potato slices that you can use for another purpose.
• This dish can be made in advance and reheated, covered, in the oven or microwave.