Heat the oven to 325. Lightly oil a large gratin dish or a baking dish (9 by 13 inch).
Peel off and discard any bruised or ragged outer leaves from the cabbage. Then cut the cabbage into 8 wedges. Arrange the wedges in the baking dish, they may overlap some, but do your best to make a single layer.
Scatter in the onion and carrot. Drizzle over the oil and stock. Season with salt, pepper, and the pepper flakes. Cover tightly with foil, and slide into the middle of the oven to braise until the vegetables are completely tender, about 2 hours. Turn the cabbage wedges with tongs after an hour. Don’t worry if the wedges want to fall apart as you turn them: just do your best to keep them intact. If the dish is drying out at all, add a few tablespoons of water.
Once the cabbage is completely tender, remove the foil, increase the oven heat to 400, and roast until the vegetables begin to brown, another 15 minutes or so. Serve warm or at room temperature, sprinkled with coarse salt.
I sometimes add a splash of balsamic vinegar to the cabbage to enhance it’s sweetness. In step 4, after you remove the foil, sprinkle on 1 1/2 tablespoons balsamic and turn the cabbage with tongs to distribute the vinegar, then roast for another 15 minutes, uncovered as directed.