In a bowl toss the plums, pears, cardamom, lemon juice, vanilla and half of the brown sugar.
Place the puff pastry on the lined sheet pan and with a sharp knife cut just the top and no more than hallway through the dough a smaller rectangle in the dough about ½ inch inside the dough.
Sprinkle the remaining brown sugar on top of the puff pastry within the smaller rectangle along with ½ tablespoon of the almonds.
Alternating pears and plum slices arrange the slices to cover all of the brown sugar. Top with the remaining almonds.
Bake for 15-20 minutes or until the puff pastry is a nice golden brown color. Top with sliced almonds and Maldon salt.