Preheat the oven to 350°F (175°C) with the rack in the center. Using a sharp knife, cut the sourdough loaf in a grid pattern, making sure not to slice all the way through so the filling stays inside.

In a small bowl, mix melted butter with garlic powder, salt, and pepper. Drizzle the butter mixture into each cut, then gently stuff pieces of brie and spoonfuls of cranberry sauce into the openings for even distribution. Sprinkle chopped parsley over the top.

Wrap the loaf in foil and bake for 15 minutes. Carefully unwrap and bake an additional 10 minutes until the cheese is melted and bubbly and the crust is lightly golden. Let the bread cool slightly before serving so it can be pulled apart easily.