Preheat the oven to 375 degrees F. In a large bowl combine all the ingredients, tossing to coat. Season with salt and pepper. Put the potato mixture into a casserole dish
, flatten it out with a spatula
, and bake for 40 minutes, until the potatoes are tender and the gratin
is bubbly. Let stand for 10 minutes before serving. Garnish
with fresh chives.