Preheat your oven to 400°F (205°C). Line a heavy rimmed baking sheet with unbleached parchment paper. Ensuring the oven is thoroughly preheated is vital for puffing up crisp, shatteringly light pastry layers.

In a medium mixing bowl, beat softened cream cheese, powdered sugar, vanilla bean paste, and fresh lemon zest with a fork or hand mixer until silky smooth and lump-free (about 60 seconds). In a separate small bowl, gently toss fresh blueberries with 1 tbsp granulated sugar, lemon juice, and cornstarch until glistening.

Unroll chilled puff pastry sheet onto a lightly floured surface or parchment paper. Cut into 6 equal rectangles. Using a sharp paring knife, gently score a 1/2-inch border around the perimeter of each rectangle without cutting all the way through the dough. Dock the inner rectangle 4 to 5 times with a fork to prevent the center from rising.

Spoon about 1 1/2 tablespoons of the vanilla cream cheese mixture into the center of each scored rectangle, spreading it evenly within the scored borders. Spoon 1 to 2 tablespoons of tossed blueberries directly over the cream cheese layer.

Brush the outer 1/2-inch pastry borders generously with the beaten egg wash. Sprinkle coarse turbinado sugar heavily over the brushed borders for that signature Parisian bakery crunch.

Transfer the baking sheet to the middle rack of the preheated oven. Bake at 400°F (205°C) for 12 to 14 minutes, until the pastry edges have puffed dramatically high into crisp golden-brown layers and the blueberries are warm, bubbling, and bursting.

Remove from oven and let rest on the baking sheet for 5 minutes. In a small ramekin, whisk powdered sugar, milk, and vanilla until smooth; drizzle zigzag across the warm pastries (or dust simply with powdered sugar). Serve warm with hot coffee!