Heat oven to 400°F; line a baking sheet with parchment. Keep pastry cool until assembly.
Unfold pastry and cut into 16 equal squares; place them on the sheet.
Mix the filling ingredients (finely diced ripe pear, crumbled blue cheese) in a bowl. Add about 1 teaspoon to the middle of each square; do not overfill.
Fold each square corner-to-corner to form a triangle, press edges with a fork, and brush with beaten egg mixed with water.
Bake 17–20 minutes until puffed and deeply golden; let cool 5 minutes before serving.