Add the remaining 2 tablespoons oil, onion, garlic, caraway seeds and cumin seeds to the pan; cook, stirring, until starting to soften and brown, 2 to 3 minutes. Add tomato paste and cook, stirring, until starting to darken, about 2 minutes. Add broth, dry mustard and the remaining 1/4 teaspoon each salt and pepper; increase heat to medium-high and bring to a boil. Return the cabbage to the pan, overlapping the wedges if necessary. Bake, turning once, until the cabbage is very soft and the sauce has reduced and thickened, 40 to 45 minutes. Sprinkle with parsley and serve with mustard, if desired.