Preheat oven to 180°C. Melt butter in a small, heavy-based saucepan and add garlic. Cook over low heat for 2-3 minutes until garlic is fragrant, but not browned. Stir in parsley
Cut sourdough loaf into a diamond pattern, cutting deeply, but leaving the base intact. Brush garlic butter on cut surfaces inside loaf, then fill with cheese.
Wrap loaf in foil and bake for 10 minutes. Remove foil and cook for a further 10 minutes until cheese is melted and loaf is golden.