Roll out the puff pastry, with a silicone baking mat or parchment paper on top to prevent sticking, until it is 11 by 11 inches. Place the puff pastry on a piece of parchment or silicone baking mat that is on a baking sheet.
Place the whole brie wheel in the center of the puff pastry.
Spread the jam on top of the brie, almost to the edges.
Add the blackberries on top of the brie, piled up as needed.
Sprinkle 1/2 teaspoon of the fresh thyme on top of the blackberries.
Beat the egg in a small bowl.
Pull one corned of the puff pastry up and over the brie, snuggly against the cheese.
Using a basting brush, brush the egg onto the puff pastry that is folded up onto the brie. This will help the following pieces stick together.
Repeat pulling edges of the puff pastry up onto the brie, brushing each section with egg, all the way around the brie.
Remove excess puff pastry dough that has collected at the top of the brie wheel.
If desired, use small cookie cutters or pie dough cutters to cut shapes out of the excess dough. Apply the shapes with extra egg under and on top of the shapes.
Brush additional egg on any exposed puff pastry that is still dry.
Sprinkle the remaining fresh thyme across the top of the puff pastry.
Bake the brie for 25-30 minutes until the puff pastry is cooked and golden.
Remove and serve immediately with crostini bread slices, apple wedges, or crackers.
This appetizer goes much further than 6 if you are serving other foods.Keep a close eye on the pastry as it is baking to ensure it is not getting too dark.Use full fat brie, not light brie. Light brie does not melt.For a berry heavy appetizer, use a full 6 ounce package.