Sweet Potato Leek Gratin

This is a recipe of Melissa Clark's from the NYT. Her recipe called for white potatoes but I only had sweet on hand and it turned out just yummy. Next time, I'll try it her way.

2 large sweet potatoes, peeled and sliced in 1/8 slices. (I used my mandoline for this job)
2 leeks sliced lengthwise and then chopped and washed well cause leeks are filled with dirt!!
2 cloves garlic minced
1 cup heavy cream
salt and pepper
thyme
nutmeg
2 T butter
3/4 cup shredded gruyere

Spray a deep dish pie pan or 2 qt gratin dish
preheat oven 350

In skillet, melt butter and sauté leeks 7 minutes, seasoning well with salt and pepper. Divide the potatoes and layer half in the bottom of the dish, add half the leeks, then the rest of the potatoes and top with the rest of the leeks. In skillet you cooked the leeks, add the cream and the garlic and few dashes of thyme and nutmeg and simmer for five minutes. Then pour over potato/leek mixture and top with cheese. Cover with foil and bake 40 minutes, then uncover and bake for 20 minutes. Let stand a while before cutting.