Crispy potato roast

I guess we never added this to the blog. We made the recipe from The Bitten Word several months ago and it was really tasty.

3 tbs unsalted butter, melted
3 tbs extra-virgin olive oil
4 lbs russet potatoes, peeled
4 shallots, thickly sliced lengthwise
course salt
1/2 to 1 teaspoon red-pepper flakes (optional)
8 sprigs thyme

In a small bowl, combine butter and oil.
Brush bottom of a round 9-inch baking dish with some butter mixture.
With a sharp knife or mandoline, slice potatoes very thinly crosswise.
Arrange potato slices vertically in dish.
Wedge shallots throughout.
Sprinkle with salt and red-pepper flakes (if using); brush with remaining butter mixture.
Bake 1 1/4 hours at 375.
Add thyme and bake until potatoes are cooked through with a crisp top, about 35 minutes more.