Red Cabbage With Walnuts and Feta Recipe

While the cabbage is roasting, prepare the vinaigrette: In a small bowl, whisk together apple cider vinegar, mustard and ½ teaspoon salt until the salt dissolves. Whisk in 3 tablespoons olive oil until the vinaigrette is emulsified. Taste for seasoning, adding more salt or vinegar if needed; it should be punchy and bright.