Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Take the crusty bread and make horizontal and vertical cuts into the loaf, ensuring not to cut all the way through. Aim for about 1-inch squares, creating a grid pattern.
Cut the Brie cheese into small wedges and carefully insert them into the cuts of the bread, spreading them evenly throughout the loaf.
If using fresh cranberries, roughly chop them; if using cranberry sauce, you can dollop it into the cuts. Ensure that cranberries are evenly distributed.
In a small bowl, melt the unsalted butter. Then, add the minced garlic, chopped rosemary, salt, and pepper, stirring to combine.
Use a basting brush to drizzle the seasoned melted butter mixture generously over the bread, ensuring it seeps into the cuts and covers the exposed surfaces.
Wrap the bread in aluminum foil, leaving the top exposed to allow for crustiness. Place it on the prepared baking sheet.
Bake in the oven for 20 minutes, then remove the foil and bake for an additional 5 minutes to achieve a golden crust.
Remove from the oven and allow to cool for a few minutes before serving. Pull apart and enjoy!