Creamy Potato Gratin

Place potatoes in a large stockpot or Dutch oven; cover with cold salted water. Bring to a boil; reduce heat, cover and simmer until potatoes are tender, about 5 minutes. Drain well; set aside.

Preheat oven to 375 degrees F. Lightly oil a 9 x 13 baking dish or coat with nonstick spray.

Melt butter in a Dutch oven over medium heat. Add garlic and shallot, and cook, stirring frequently, until tender, about 3-4 minutes.

Whisk in flour until lightly browned, about 1 minute. Gradually whisk in chicken stock and heavy cream. Bring to a boil; reduce heat and simmer, stirring constantly, until reduced and thickened, about 5 minutes.

Remove from heat; stir in 3/4 cup white cheddar cheese and mustard. Stir in potatoes; season with salt and pepper, to taste.

Spread potato mixture into the prepared baking dish. Place into oven and bake until potatoes are tender and mixture has thickened, about 35-40 minutes.

Sprinkle with remaining 1 1/4 cups white cheddar cheese. Place into oven and broil until golden brown, about 3 minutes. Let stand 5 minutes.

Serve immediately, garnished with chives, if desired.