2 tablespoons butter
1 onion, minced
2 garlic cloves, minced
1 tablespoon fresh thyme leave, minced
1 1⁄4 teaspoons salt
1⁄2 teaspoon ground black pepper
2 1⁄2 lbs russet potatoes or 5 medium russet potatoes, peeled and sliced 1/8-inch thick
1 cup low sodium chicken broth
1 cup heavy cream
2 bay leaves
4 ounces cheddar cheese, shredded
Adjust an oven rack to the middle position and heat the oven to 425 degrees.
Melt the butter in a Dutch oven over medium-high heat. When the foaming subsides, add the onion and cook, stirring occasionally, until soft and lightly browned, about 4 minutes.
Add the garlic, thyme, salt, and pepper and cook until fragrant, about 30 seconds. Add the potatoes, broth, cream, and bay leaves and bring to a simmer. Cover, reduce the heat to medium-low, and simmer until the potatoes are almost tender (a paring knife can be slipped into and out of a potato slice with some resistance), about 10 minutes. Discard the bay leaves.
Transfer the mixture to an 8-inch square baking dish (or other 1 1/2 quart gratin dish). Sprinkle evenly with the cheese. Bake until the cream is bubbling around the edges and the top is golden brown, about 15 minutes. Cool 10 minutes before serving.
Adapted from Cooks Illustrated