Remove one portion of the puff pastry dough from the fridge and unwrap it. Roll the dough out into a large rectangle that's roughly 8x12 inches and about 1/8 inch thick. You want the dough to be just slightly bigger than those dimensions so you can trim the sides to get nice, clean edges. It's super important that the dough is rolled to be 1/8 of an inch, or else it won't bake through in the center.
Then cut the rolled dough into 8 equal-sized squares or rectangles that are about 2x3 inches (you can cut these into any shape as long as they're all the same size). Place the dough on a baking sheet lined with parchment paper or a silicone mat.
Use a paring knife to score (partially cut) a smaller rectangle inside the pastry. Be careful not to cut all the way through. The lines should be about 1/2 inch or 1.5cm from the edge of the pastry.
Then pipe or spoon a couple of Tablespoons of cream cheese filling in the center of each rectangle.
You can bake these without any other toppings, but I like to add a bit of fruit (I usually use fresh berries or sliced canned pears) or ham & freshly grated gruyere.
Beat together 1 large egg and 1 Tbsp of water in a small bowl, then brush around the edges of the pastry. Top with coarse sanding sugar (omit for savory pastries).
Bake in the pre-heated oven for 18-20 minutes, or until the pastry is a deep golden brown and the edges have puffed up. If it seems like the pastry is over-browning or if your oven runs a bit hot, cover the pastries with foil for the last few minutes. Let the pastries cool on the pan for about 10 minutes, then enjoy.
While the first batch bakes, remove the remaining portion of the dough from the fridge and repeat steps 1-7.