Preheat oven to 350 degrees. Lighty spray or butter a 9x13-inch baking dish. Arrange potatoes by fanning them in three lines across the pan. Set aside.
In a medium saucepan set over medium heat, add the butter. Once melted add the onion and saute for 3-5 minutes or until tender. Add the garlic and continue cooking for 1 additional minute.
Whisk in the flour, cook until lightly golden in color, then slowly pour in the half & half, whisking until all of the liquid has been incorporated. Whisk in salt and pepper.
Pour mixture over the potatoes. Top with cheese.
Cover with aluminum foil and bake for 45 minutes. Remove the foil and continue baking for 15-30 minutes or until golden brown and potatoes are fork-tender.
Let cool for 15 minutes before serving. Top with fresh chives, if desired.