Preheat oven to 350ºF. Place brie in a baking dish and set aside.
In a skillet, brown pancetta and onion until pancetta is crisp. Add plum and cook 1 minute. Season with pepper.
Deglaze the pan by adding sherry. Simmer 1 minute, remove from heat and stir in pistachios. Pour over the brie.
Cover with foil and bake for 20-25 minutes or until cheese has melted. Serve immediately with crackers or toasted bread. Makes 6 to 8 servings.