French Onion Potato Gratin

Instructions

Position a rack in the middle of the oven and crank the heat to 375°F (190°C). Generously butter a 2-quart (1.9 L) casserole dish.

In a large skillet over medium-high heat, melt the butter.

Scoop in the mushroom and onion slices and stir to coat. Season with salt and pepper. Continue to cook, stirring occasionally, until the mushrooms and onions are softened and browned, 13 to 15 minutes.

Toss in the garlic and thyme and cook until fragrant, 1 to 2 minutes. Stir in the nutmeg. Remove the skillet from the heat.

Using a mandoline or sharp knife, carefully cut the potatoes into 1/8-inch (3 mm) thick slices.

Line the bottom of the prepared casserole dish with a double layer of potato slices, overlapping slightlyâ€"kind of like playing cards. Sprinkle lightly with salt and pepper.

Scoop about 1/3 of the mushroom-onion mixture into the dish and spread over the potatoes. It won’t cover it fully, but that’s okay.

Sprinkle 1/3 of the cheese over the top.

Repeat layering the potatoes, salt and pepper, mushroom-onion mixture, and cheese, two more times.

Slowly pour the cream into a crevice along the side, being mindful not to wash away the cheese on top.

Slide the casserole into the oven and bake until the potatoes are fork-tender and the top is golden brown, 50 to 60 minutes. If the top browns too quickly, cover it with foil halfway through baking.

Remove the casserole from the oven and let sit for 20 minutes before serving.

Sides