- Prep time
- 30–40 minutes PT40M
- Cook time
- 1 hour 30 minutes PT30.016666666667M
- 8–10 servings
This classic dish gets an extra-decadent makeover with a rich mushroom and Parmesan cream sauce plus fresh thyme for a fragrant finish.
- 2 shallots, sliced thin
- 1 clove garlic, crushed
- 2 tablespoons butter
- 1 bunch thyme, picked and chopped, stems reserved
- ½ cup marsala
- ½ ounce dried porcini mushrooms
- 2 cups milk
- 3 cups heavy cream
- 1¼ cups grated Parmesan cheese, divided
- 1 tablespoon salt
- ¼ teaspoon white pepper
- 3 pounds large Yukon gold potatoes
Sauté the shallots and garlic in butter until translucent. Add thyme stems, deglaze with the marsala and add the dried mushrooms. Reduce until almost dry then add the milk and cream. Bring to a simmer and then remove from heat and let steep for 10 minutes.
Remove thyme stems from hot cream mixture, then transfer to a blender, add 1 cup Parmesan cheese and puree on high for 30 seconds. (This may need to be to be done in batches depending on the size of your blender.) Strain through a fine mesh strainer into a large work bowl. Season with salt and white pepper.
Use a mandolin or knife to slice the potatoes no more than ⅛ inch thick, then place in the mushroom cream and toss gently to coat. Shingle a single layer of the coated potatoes into a casserole dish then top with ½ teaspoon chopped thyme. Repeat the layering process until the potatoes are about ½ inch from the top of the dish. Add any porcini cream left in the bowl just to cover the potatoes.
Heat oven to 400°F.
Cover the dish with foil and bake for about 1 hour, or until the potatoes are tender and a knife slides easily into the center.
Remove foil, sprinkle with ¼ cup Parmesan cheese and a pinch of thyme, and bake uncovered for 10 minutes until top browns. Let rest 10 minutes before serving.