Seasonal Potluck: Sweet Potato and Yukon Gold Potato Gratin

I am very unhappy with the lack of daylight since we’ve set the clocks back.  It means I need to either figure out how to take some decent looking pictures in artificial light (which I should) or cram all of my cooking into the daylight hours on the weekends.

The month of sweet potatoes continues!  This gratin is a nice comfort food side dish, and the sweet potatoes put a nice twist on it.  It makes a TON though, so feel free to halve the recipe if necessary.

Sweet Potato and Yukon Gold Potato Gratin

adapted from Epicurious, makes 12 servings

• 6 tablespoons (3/4 stick) butter, room temperature,  divided
• 2 1/4 pounds Yukon Gold potatoes, rinsed
• 1 1/2 pounds red-skinned sweet potatoes (yams),  peeled
• 2 cups whole milk
• 1 garlic clove, pressed
• 1 tablespoon kosher salt
• 2 teaspoons fresh thyme leaves
• 1 teaspoon ground black pepper
• 1/8 teaspoon ground nutmeg

Preheat oven to 400°F. Coat 13x9x2-inch glass baking dish with 2 tablespoons  butter. Thinly slice all potatoes; place in prepared dish. Bring milk and next 5  ingredients to boil in medium saucepan; pour over potatoes. Dot with 2  tablespoons butter. Cover with foil. Bake until potatoes are tender and milk is  almost absorbed, about 1 hour.