Mashed Potato Casserole

3 lbs potatoes, peeled and cut into 1-inch chunks
1/3 C half and half
1/3 C chicken broth
1/2 C unsalted butter, cut into cubes
1 small garlic clove, minced
1 1/2 tsp Dijon mustard
1 1/2 tsp salt
3 large eggs
2 T finely chopped fresh chives, optional

Heat oven to 375 degrees. Bring potatoes and water to cover by one inch to boil in large pot over high heat. Reduce heat to medium and simmer until potatoes are tender, about 20 minutes. Heat the half and half, chicken broth, butter, garlic, mustard, and salt in saucepan over medium-low heat until smooth, about five minutes. Keep warm. Drain potatoes and transfer to bowl of stand mixer fitted with paddle and mix on medium-low speed, slowly adding half-and-half, until smooth, about one minute. Beat in eggs one at a time for about one minute. Add in chives. Transfer potato mixture to greased two-quart baking dish and use fork to make peaked design on top. Bake until potatoes rise and begin to brown, about 35 minutes. Let cool for ten minutes. Serve.