Preheat oven to 400 degrees F. Saute onion and garlic in butter until golden. Set aside. Put Brie and cream cheese in a bowl and microwave until soft. Mix in onion and garlic, sour cream, lemon, brown sugar and Worcestershire sauce; season to taste with salt and pepper. Hollow out the middle of the loaf and fill with mixture. Wrap in foil and bake in oven until bubbly, about 1 hour. Dust with paprika, optional. Serve hot with bread pieces or crackers.