Muffin-Tin Potatoes Gratin

Preheat oven to 350 degrees F. Coat 12 standard-size muffin cups with cooking spray. Use a mandoline to slice potatoes into 1/8-inch-thick rounds (you should have about 4 cups). Set aside.

Melt butter in a small saucepan over medium heat. Add shallots, garlic and herbs. Cook, stirring often, until the shallots are slightly softened, about 3 minutes. Add 3/4 cup milk; heat until steaming. Meanwhile, whisk flour and the remaining 1/2 cup milk in a small bowl until smooth; stir into the hot milk mixture and cook, whisking constantly, until the sauce thickens, about 2 minutes. Remove from heat and gradually whisk in 3/4 cup cheese. Whisk in vinegar, salt and pepper; transfer the mixture to a large bowl. Remove and discard the garlic clove. Add the potatoes and toss, separating any slices that stick together, until well coated.

Spoon about 1/3 cup potato mixture into each prepared muffin cup. Top evenly with the remaining 1/4 cup cheese. Cover the muffin pan with foil and bake until the potatoes are tender, about 35 minutes. Let cool for 5 minutes. Garnish with additional herbs, if desired. If needed, run a knife around the edges of the muffin cups to loosen the gratins before serving.