Put brie in an oven proof pan and bake for 10 minutes until just starting to melt.
While brie is warming, melt butter and brown sugar in pan and stir until melted.
Add juice and stir until incorporated.
Add in blackberries, stir until berries are warm; mash a couple to add some color to the sauce. Add the chopped nuts to the mixture and remove from stove-top.
Remove brie from oven and top with fruit and nut mixture; scatter raspberries over the top.
Serve with baguette slices and grapes or apple slices.
Notes
Toasted Walnuts
Place walnuts on an oven proof plate in a single layer and toast in toaster oven or regular oven for 4-6 minutes, stirring halfway. Watch carefully!