Take the puff pastry out of the freezer. Set on the kitchen counter to thaw.
Preheat the oven to 375F.
Rinse the spinach well to remove any trace of soil. Drain.
Blanch the spinach in a pot of boiling water for five minutes. Drain. Dump in a bowl of iced water to cool. Alternatively, pour into a strainer and place under the tap for about thirty seconds. Drain then squeeze out the excess water (see detailed instructions).
Roughly chop the spinach.
Drain the artichokes and roughly chop.
Place the chopped spinach and artichokes in a mixing bowl. Crumble the kesong puti and grate the mozzarella over them. Add the sour cream, salt, pepper, and lemon and pepper seasoning. Stir well.
Roll out the thawed puff pastry to a thickness of a quarter inch. Trim the sides to make a neat rectangle.
Carefully transfer the rolled puff pastry on a lined baking tray (see tip).
Brush all the edges of the crust with egg wash.
Fold in all sides of the crust, about 1 cm wide, to make a ridge on every side.
Pierce the bottom of the crust several times with a fork to create steam vents to prevent the crust from rising during baking.
Spread the artichoke spinach filling evenly on the crust without going over the ridges.
Brush the top of the ridges with more egg wash.
Bake the tart in a 375F oven for 30 to 40 minutes or until the ridges of the crust are puffed and browned.
Cut the cheesy artichoke and spinach tart into rectangles or squares. Serve hot.