01 -
Preheat oven to 375°F (190°C). In a small bowl, combine melted butter and olive oil. Brush the bottom of a round 9-inch baking dish with some of the butter mixture.
02 -
Using a sharp knife or mandoline, slice the potatoes very thinly crosswise.
03 -
Arrange potato slices vertically in the baking dish. Wedge shallots throughout the arrangement. Sprinkle with coarse salt and red-pepper flakes, if using. Brush the potatoes and shallots with the remaining butter mixture.
04 -
Bake the dish for 1 hour and 15 minutes at 375°F (190°C).
05 -
Add thyme sprigs over the potatoes and bake for an additional 35 minutes, or until the potatoes are fully cooked with a crisp golden top.