Idaho Potato Commission

1 cup heavy whipping cream
1 cup half and half
1 (5.2-ounce) package Boursin cheese with garlic and herbs
1 1/4 teaspoon kosher salt
2-3 tablespoons finely minced Italian flat parsley (about 1/3-1/2 cup leaves measured before mincing)
3 fat garlic cloves, crushed or finely minced
1 (9- to 10-ounce) container frozen chopped spinach, thawed and squeezed dry
3 pounds Idaho Russet potatoes (or Idaho Yukon Gold potatoes), peeled, thinly sliced (about 1/8-inch-thick slices)
Freshly ground pepper
4-6 ounces Gruyere, shredded

Heat oven to 400° F. Butter (or mist with nonstick spray) a 9- by 13-inch baking dish with 2-inch-high sides, and set dish aside.
In a heavy medium-sized saucepan, heat cream, half and half, Boursin cheese and salt over low heat until cheese melts and mixture is smooth, stirring frequently. Sauce will thicken just slightly as it heats. (Keep an eye on this so it doesn’t boil over, which will make a huge mess on your stove! Trust me on this.) When sauce is melted and mixed, remove pan from heat and stir in the parsley, garlic and spinach.
Arrange half of sliced potatoes in prepared baking dish. Generously season potatoes with pepper. Ladle half of sauce mixture over, and sprinkle on half the Gruyere. Arrange remaining potato slices atop first layer in dish, creating a pretty overlapping shell pattern if you like. Season again with a grinding of fresh pepper. Ladle remaining sauce mixture over potatoes, and sprinkle on the rest of the Gruyere. Bake until top is golden brown and potatoes are tender when pierced with knife, about 50-55 minutes.
Remove from oven and serve, or place hot dish on a buffet table and allow diners to serve themselves.