Preheat the oven to 400 degrees F. Grease an 8 cup rectangular baking dish with 1 tablespoon butter. In a nonreactive saucepan, over medium heat, melt the remaining butter. Stir in the flour and cook for 2 minutes. Whisk in the milk and cook until the liquid is slightly thick and coats the back of a spoon, about 4 to 6 minutes. Season with salt and pepper. Remove from the heat. In a mixing bowl, toss the sliced new potatoes with salt and pepper. Fold in the cream sauce and pour into the prepared pan. Sprinkle the top of the potatoes with the grated cheese. Place the pan in the oven and bake until golden brown and bubbly, about 8 to 10 minutes. Remove from the oven and cool for a couple of minutes before serving.