Potato and Mushroom Gratin — With A Japanese Twist

A potato and mushroom gratin made with miso.
A potato and mushroom gratin made with miso.

At this time of year, a potato gratin is almost de rigueur.

And over the years, I’ve made countless variations on them.

This particular one for “Potato and Mushroom Gratin” caught my eye because it includes a novel ingredient: miso.

The recipe is from “Make It Japanese” (Clarkson Potter), of which I received a review copy.

The cookbook is by Rie McClenny, a culinary content creator and graduate of the French Culinary Institute who created viral food videos for BuzzFeed Tasty. Born in Hiroshima, she now lives in Los Angeles. It was written with Sanae Lemoine, a former cookbook editor for Phaidon and Martha Stewart.

The recipes draw from the food she learned to cook from her mother, as well as dishes she’s developed over the years for her family.

They include “Curried Kabocha Croquettes,” “Rolled Omelet,” “Creamy Soy Milk Udon with Pork and Bok Choy,” and “Matcha Tiramisu.”

This gratin features thinly sliced russets, cremini mushrooms, and onions that are first briefly sauteed, then arranged in a baking dish before adding a bechamel sauce, then topping with shredded mozzarella, grated Parmesan, and panko.

Thinly sliced potatoes, onions and cremini go into a baking dish before adding the bechamel.
Thinly sliced potatoes, onions and cremini go into a baking dish before adding the bechamel.

It all gets baked in the oven until the potatoes are cooked through, the cheese melts, and the top is golden.

I can’t say this dish came off without a hitch. I found there was way too much excess liquid after cooking, leaving the potato-mushroom mixture looking soupy.

The bechamel in this recipe is made with 3 cups whole milk and 1/4 cup flour. At first, I worried that I didn’t cook the sauce long enough allowing it to thicken further. However, I later consulted other bechamel recipes, including one by Jacques Pepin. They all had a higher proportion of flour to milk, about 2 tablespoons of flour to 1 cup of milk or in Pepin’s case, 3 tablespoons of flour to 1 1/2 cups of milk. Using his ratio, that meant for 3 cups of milk, he would have added 3/8 cup of flour.

When I poured the bechamel into the pan, it completely covered the potato-mushroom mixture and then some. If I made this again, I would cut the amount of milk to 2 1/2 cups instead, and use 1/4 cup plus 1 tablespoon of flour.

While the miso addition drew me to this recipe in the first place, both my husband and I didn’t really notice it in the final dish. The recipe didn’t specify what type of miso to use, so I used white. It’s possible that if you use the more pungent brown miso, the taste will be more pronounced.

However, since there is no other salt used in this recipe, I think you can easily increase the amount of miso. The recipe calls for stirring 3 tablespoons of miso in the bechamel. I would up that to at least 4 tablespoons or to taste.

I was surprised that the recipe also didn’t specify to let the gratin sit for at least 15 minutes out of the oven before serving — usually standard with creamy gratin dishes — to allow the sauce time to cool down a little and further thicken and cling to the vegetables. I did let mine sit that long and there was still too much liquid.

The gratin was still too soupy after sitting for more than 15 minutes, so that's why I added some changes to the recipe for when I make it again.
The gratin was still too soupy after sitting for more than 15 minutes, so that’s why I added some changes to the recipe for when I make it again.

So, I’ve added those changes to the recipe below. I do love the combination of potatoes and mushrooms in this dish for their earthy flavors. With a little bit more miso, this dish should take on a nice meatiness plus a deep savoriness, giving a classic gratin a delicious new twist.

Potato and Mushroom Gratin

(Serves 6 as a side)

For the filling:

1 tablespoon neutral oil, such as canola or grapeseed

1 white onion, thinly sliced (about 2 cups)

2 russet potatoes (about 1 pound), peeled and sliced 1/8-inch thick

6 ounces cremini mushrooms, sliced (about 2 cups)

For the bechamel sauce:

4 tablespoons (1/2 stick) unsalted butter

1/4 cup plus 1 tablespoon all-purpose flour

2 1/2 cups whole milk, at room temperature

4 tablespoons miso or to taste

For toppings:

1 cup shredded mozzarella cheese (about 4 ounces)

1/4 cup grated Parmesan cheese (about 1 ounce)

1/4 cup panko bread crumbs

Coarsely chopped fresh parsley leaves, for garnish

Preheat the oven to 350 degrees.

Make the filling: In a large skillet, heat the oil over medium heat. Add the onion and cook, stirring until translucent, about 10 minutes. Add the potatoes and cook, stirring until the edges are slightly translucent, about 5 minutes. Add t he mushrooms and cook, stirring until softened, 2 to 3 minutes. Transfer the mixture to a 2-quart baking dish (about 8-by-10 inches) and set aside.

Make the bechamel sauce: In a medium saucepan, melt the butter over medium heat. Sprinkle the flour over the butter. Cook, whisking, until bubbly, 2 to 3 minutes. While whisking constantly, slowly pour in the milk. Whisk in the miso and bring to a boil; this can take up to 25 minutes. Reduce the heat to medium-low and simmer, stirring often, until the sauce thickens, 10 to 15 minutes. Pour the bechamel over the potatoes.

Top the gratin: Sprinkle with the mozzarella, Parmesan, and panko. Cover with foil, and place the dish on a baking pan in case of any drips. Bake, rotating the baking dish front to back halfway through, for 45 minutes. Remove the foil and bake until the top is golden brown, 15 to 20 minutes. Remove from the oven, and allow to sit for about 15 minutes. When ready to serve, garnish with parsley.

Tip: Make sure the milk is at room temperature; otherwise, the bechamel might curdle.

Adapted from “Make It Japanese” by Rie McClenny

More Potato Dishes for the Holidays: Sweet Potato Salad with Cumin, Smoked Paprika, and Almonds

And: Crispy Semolina Potatoes

And: Miso-Maple-Jammed Sweet Potatoes

And: See’s Scotch Kiss Sweet Potatoes

And: Smashed Yukon Gold Potatoes

And: Two-Scalloped Potatoes with Chimichurri

Plus A Cauliflower Dish: Modern Cauliflower Gratin

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