Begin by preheating your oven to 360°F (180°C) to ensure it's ready when the bites are assembled. While the oven heats, carefully cut the brie cheese into small cubes, as it will be easier to handle at room temperature. Then, tear the thinly sliced prosciutto into smaller, bite-sized pieces; I find this texture works better than cutting it for these types of appetizers.

Thoroughly grease a mini muffin pan with butter. Lay one sheet of phyllo pastry flat, brush lightly with melted butter, then top with a second phyllo sheet, brushing again, and finally a third sheet. Cut the layered phyllo into 2-inch by 1-inch rectangles, then gently press each rectangle into the cups of the prepared mini muffin pan, creating a cup shape.

Into each phyllo cup, spoon about 1 teaspoon of cranberry sauce. Then, add a few pieces of the torn prosciutto and several cubes of brie cheese on top of the cranberry sauce. This layering helps to distribute the flavors evenly. Bake for approximately 10 minutes, or until the phyllo is golden brown and crispy, and the brie is beautifully melted and gooey.

Carefully remove the baked cranberry brie prosciutto bites from the oven and allow them to cool slightly in the muffin pan before transferring them to a serving platter. While they're still warm, sprinkle thinly chopped fresh rosemary over the top; I find the aroma of fresh rosemary really elevates the dish. Serve these delightful bites warm to best enjoy the melted cheese and crispy phyllo.