Start by preheating your oven to 200°C (400°F). Cut the cabbage into four equal wedges, keeping the core intact so the wedges hold their shape while roasting.
In a small bowl, mix two tablespoons of softened butter with the miso paste until smooth. This mixture should be spreadable and evenly combined.
Place the cabbage wedges on a baking sheet and generously coat all sides with the miso butter. Roast in the oven until the cabbage is tender with golden, slightly charred edges.
While the cabbage roasts, melt the remaining butter in a skillet. Add the panko breadcrumbs and garlic powder, stirring until the crumbs turn golden and crisp.
Remove the cabbage from the oven and sprinkle with toasted breadcrumbs. Garnish with fresh parsley if desired and serve immediately while warm