To make the walnuts, melt butter, brown sugar, and cinnamon together in a small saucepan over low heat until sugar is completely dissolved. Stir in walnuts, making sure to coat all of them. Pour onto wax paper to cool completely.
Preheat oven to 350F.
Place phyllo cups on a lined baking sheet. Place a piece of brie into each cup. Bake for 5 - 8 minutes, until brie has softened but not melted completely. Divide cranberry sauce between the cups. Sprinkle with candied walnuts.