Toss strawberries in balsamic vinegar and black pepper and set aside. Preheat skillet over medium heat. Lightly toast bread slices on 1 side and remove from skillet. Top toasted side of each slice with 3 slices of Brie and 1/4 of the candied pecans. Top 2 of these slices with basil, strawberries and prosciutto. Cover with remaining 2 bread slices, untoasted-side-up. Melt half the butter in skillet over medium heat. Place sandwiches in skillet and butter tops with remaining butter. Grill sandwiches, flipping, until Brie has melted and bread is golden brown