Slice the brie in half across the middle. Spread the cooked leek and tomato mixture onto one half of the brie and sprinkle with the crisp bacon. Top the leek and bacon mixture with other half of the brie, rind facing up.
Spread the puff pastry sheet onto a counter and roll it to an eighth of an inch thick and into a square that measures 10x10”. Place the filled brie in the middle of the puff pastry and wrap the dough up and over the brie, starting at the corners. Invert onto a sheet pan lined with parchment.
Mix up egg and 2 tablespoons water and brush the top and sides of brie. Make 3 tiny slits in the middle to allow steam to escape during cooking.