I admit right off: I used 1/2 shallots and 1/2 the sweet yellow onions (since they've been on sale...and they're delicious...and I had lots. :)
3 Tbls unsalted butter*
1 1/2 lbs shallots, peeled, thinly sliced
4 lbs potatoes
1 Tbls freshs thyme leaves
(and sprigs for garnish if desired)
1/2 tsp each salt and pepper
2 C heavy cream or half-and-half
1 C Gruyere cheese, shredded
Preheat oven: 375°
1. Melt 3 Tbls butter in skillet over medium low heat; add shallots. Cook, stirring frequently, 25-30 minutes until golden and tender.
2. Grease/spray a 3-quart casserole dish. Peel and thinly slice potatoes.
3. Place potatoes, shallots, thyme, salt and pepper in a large bowl. Toss lightly to coat potatoes. Transfer to casserole.
4. Heat cream in a saucepan until it just comes to a simmer; pour over potato mixture. Bake 30 minutes.
5. Sprinkle Gruyere over top; bake 20 minutes more or until potatoes are tender and top of casserole is brown and crusty.
* I do buy and use unsalted butter. However, when the recipe--like this one--calls for salt and other salty ingredients...I'm not adamant about it!