Preheat the oven to 400 degrees F (200 degrees C).

Pour olive oil into a heavy baking dish (such as an enameled cast iron dish). Place potatoes into the baking dish and toss to coat. Sprinkle with red bell pepper, thyme sprigs, kosher salt, black pepper, and cayenne pepper.

Bake in the preheated oven for 30 minutes. Toss vegetables to turn over. Some potatoes may stick; don’t try to turn them. Return to the oven and bake for 20 more minutes.

Toss vegetables again, turning potatoes so the unbrowned sides come into contact with the bottom of the dish. Continue baking until potatoes are browned and tender, about 15 more minutes.

Turn the oven off and leave potatoes in the oven for 15 more minutes. Toss once more. Season with salt, black pepper, and cayenne pepper before transferring to a serving bowl.