Blue Cheese Potatoes au Gratin

5 lbs. russet potatoes
2 tsp. salt
1/2 tsp. black pepper
1-1/2 tsp. fresh rosemary, minced
3/4 cup crumbled blue cheese
3/4 cup grated parmesan cheese
1 cup sour cream
2 cups cream
1 tsp. salt

Preheat oven to 350 degrees F.

1. Butter a 9- by 13-inch glass baking dish. Peel and slice the potatoes into 1/4-inch slices. Toss them in a large bowl with the 2 teaspoons salt, pepper and rosemary.

2. In a small bowl toss together cheeses.

3. Layer half the potatoes in the buttered baking dish. Sprinkle with half the cheese mixture and top with remaining potatoes.

4. In a bowl, whisk together sauce ingredients and pour over potatoes. Tap the baking dish on the counter to spread out the sauce and help release any air bubbles. Sprinkle with remaining cheese mixture.

5. Bake potatoes for about 1 hour and 15 minutes, or until browned and completely tender all the way through when poked with a knife.

Note: You can also make these in advance and store, covered and refrigerated, for up to 2 days. Bring to room temperature and reheat in a 350 degree F oven until hot.