Just chop 1 cup of walnuts (depending on the size of brie you need to cover) and stir into 1 cup crumbled blue cheese.
Press onto the top of the brie and carefully wrap a sheet of thawed puff pastry dough (Roll out to size needed).
Use fingers wet with cold water to seal underside of pastry.
Cut off excess to make cut-outs and adhere to top of brie with a little cold water.
I refrigerate my brie at this point until I'm ready to bake.
Remove from fridge, Brush w/egg wash (1 egg beaten with a tablespoon cold water) and bake on a cookie sheet covered with baking parchment in a 375F (190C) oven for about 20 minutes until golden.
(Parchment makes it simple to transfer brie to serving dish.)