Thaw your puff pastry in the refrigerator overnight, according to the packaging directions.
Preheat your oven to 400℉.
Cut each sheet of puff pastry into 9 squares using a pizza cutter or knife.
Use a paring knife to lightly score a square 1 cm in from the edges of each piece of pastry.
Mix together the mascarpone, powdered sugar, and milk using a stand mixer or by hand.
Add 1 tbsp of the mascarpone filling to the middle of each pastry square.
Use a spoon to evenly spread the filling before brushing the edges of each pasty with the vegan egg wash.
Mix together the melted butter, brown sugar, and cinnamon and either pipe or spoon on 2 tsp on to each square.
Bake for 15 minutes, then allow to cool on the pan for 10 minutes before transferring to a rack to cool further.
Notes
When baking, the cinnamon sugar mixture will spread and make a delicious mess around each pastry. Just cut away the caramelized mixture that forms after baking before transferring the pastries to the rack to finish cooling!