- 1 tablespoon unsalted butter, at room temperature
- 1 cup heavy cream
- 3/4 cup low-sodium chicken broth
- 4 tablespoons all-purpose flour
- 1 tablespoon fresh thyme leaves, lightly chopped
- 2 1/2 pounds Idaho potatoes, peeled and sliced about 1/8 inch thick (about 5 potatoes)
- 6 ounces grated Gruyere cheese (about 2 cups)
- Kosher salt and freshly grated black pepper
- Rub the insert of a 6-quart slow cooker very lightly with the butter on the bottom and 2 inches up the sides.
- Whisk together the cream, broth, flour and thyme in a 2-cup measuring cup.
- Arrange 1/3 of the sliced potatoes in an even and slightly overlapping layer on the bottom of the slow cooker insert. Sprinkle 1/3 of the Gruyere over the potatoes, and add 3/4 teaspoon salt and an even grating of black pepper. Drizzle 1/3 of the cream mixture evenly over the layer. Repeat with 2 more layers of potatoes, Gruyere, salt, pepper and cream mixture.
- Press the potatoes down firmly to make sure they are submerged. Cover the slow cooker, and cook on high until the potatoes are tender and the liquid has thickened, 4 1/2 to 5 hours. Remove the lid, and let the potatoes rest for 15 minutes. (The sauce may seem thin at first, but it will thicken as it sits.)