Mashed Potato Casserole

Adjust an oven rack to the upper-middle position and heat the oven to 375 degrees. Bring the potatoes and water to cover by 1 inch to a boil in a large pot over high heat. Reduce the heat to medium and simmer until the potatoes are tender, about 20 minutes.

Heat the half-and-half, broth, butter, garlic, mustard, and salt in a saucepan over medium-low heat until smooth, about 5 minutes. Keep warm.

Drain the potatoes and transfer them to a large bowl. With an electric mixer on medium-low speed, beat the potatoes, slowly adding the half-and-half mixture until smooth and creamy, about 1 minute. Scrape down the bowl; beat in the eggs 1 at a time until incorporated. Fold in the chives.

Transfer the potato mixture to a greased 2-quart gratin dish. Use a fork to make a peaked design on the potatoes. Bake until the potatoes rise and brown, about 35 minutes. Let cool 10 minutes. Serve.