Preheat the oven to 375F.
Cut half a medium cabbage into four wedges and place them in a baking dish. Drizzle them with olive oil and season with salt and pepper.
Roast them in a preheated oven for 30 minutes, turning the wedges over half way through cooking time.
Just before the cabbage is ready, combine butter, prepared mustard, and onion powder in a small saucepan.
Heat over a low heat and whisk together until combined (I used a silicone whisk). Season with black pepper.
Transfer the cabbage to a serving platter, and pour the sauce over the top. Garnish with chopped fresh chives.
