Preheat your oven to 400°F and position the oven rack in the center.
Line a baking sheet with parchment paper for easy cleanup.
In a bowl, whisk together cream cheese, powdered sugar, vanilla extract, egg yolk, and a pinch of salt until smooth and fluffy.
Roll out your puff pastry sheet on the baking sheet, brushing off any extra flour.
Cut the pastry along the natural folds to make three strips, then slice each strip in half to create six even pieces.
Using a fork, prick the edges of each puff pastry rectangle, leaving about a half-inch border around the sides.
Using a fork, prick the edges of each puff pastry rectangle, leaving about a half-inch border around the sides.
This step helps prevent the center from puffing up too much.
Spoon about two heaping tablespoons of the cream cheese mixture into the center of each pastry square.
Spoon about two heaping tablespoons of the cream cheese mixture into the center of each pastry square.
Spread it evenly while keeping the edges clear.
Beat the egg white until frothy, then lightly brush it along the borders of the pastries to ensure a golden, shiny finish when baked.
Bake the pastries for 10 minutes, then rotate the baking sheet for even browning.
Continue baking for an additional 5-10 minutes, or until the edges are puffed and golden.
Remove the pastries from the oven and transfer them to a cooling rack using a spatula.
Allow them to cool.
While the danishes cool, whisk together powdered sugar, vanilla extract, and milk to create a smooth glaze.
Drizzle this over the cooled pastries.
For an optional fruity twist, you can also drizzle with strawberry jam thinned with a little water.