Place a rack in middle of oven; preheat to 425°. Drizzle 1 very large or 2 small savoy cabbages (2–2½ lb. total), halved, cut into 4–6 wedges depending on size, all over with extra-virgin olive oil; season generously with kosher salt and freshly ground pepper. Set aside.

Heat a dry cast-iron skillet over medium. Cook 4 slices thick-cut bacon (about 6 oz.), cut into ¼"-thick pieces, stirring often, until browned and crisp, 8–10 minutes. Using a slotted spoon, transfer to paper towels to drain.

Pour 2 Tbsp. extra-virgin olive oil into drippings in same skillet. Working in batches and adding more oil between batches if needed, carefully arrange cabbage wedges, cut sides down, in pan and cook over medium, turning to other cut sides halfway through, until cut sides are golden brown, 12–16 minutes per batch. Transfer to a parchment-lined rimmed baking sheet, arranging on a cut side down. Reserve skillet.

Transfer cabbages to oven and bake, turning halfway through, until deeply charred on all sides and tender, 30–40 minutes.

Meanwhile, cook 1 medium shallot, finely chopped, 4 sprigs thyme, and 4 Tbsp. unsalted butter in reserved skillet over medium, stirring occasionally, until shallot is softened, about 4 minutes. Add ¼ cup red wine vinegar, 3 Tbsp. pure maple syrup, 2 Tbsp. Dijon mustard, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt. Cook, stirring often, until sauce is reduced to a glaze-like consistency, about 3 minutes. Taste and season with pepper and more salt if needed. Using tongs, drag wedges through sauce to coat and arrange on a platter. Pour any sauce remaining in pan over and top with bacon.