Step 1Heat the oil and butter in a large saucepan over medium-high heat.
Step 2Add the leeks and cook, stirring until softened, about 2 minutes. Add the garlic and cook another 1 minute. Add the cabbage and radicchio, increase the heat to high and cook, stirring occasionally, until the cabbage is wilted and starting to brown, about 3 minutes.
Step 3Add the broth and cook until the vegetables are tender and the broth has evaporated, 4 minutes. Stir in the vinegar and cook until the vinegar has evaporated, 1 minute. Season with salt and pepper to taste.