Preheat the oven to 375 degrees F. Beat cream cheese, sugar and vanilla until smooth. Separate the egg yolk from the egg white. Add egg yolk to cream cheese mixture and beat until well combined, then set aside. Place egg white in a small bowl and beat with a fork until fluid. On a lightly floured surface, roll out the puff pastry into a 10 x 10-inch square. Cut the square into 4 quarters. Place quarters on a non-stick or parchment-lined baking sheet. Brush with beaten egg white, then refrigerate 15 minutes. Peel pears, cut in half lengthwise, scoop out the cores, and brush with lemon juice. With a paring knife, cut 5 to 6 slices into each pear half being sure not to cut all the way through. Gently press down on each pear half to fan them out. Divide and spoon the cream cheese mixture into the centre of each piece of puff pastry. Top cream cheese mixture with a pear half. (Can be made to this stage several hours in advance and kept in the fridge until needed). Bake 25-30 minutes, or until puff and golden. Cool on baking rack 15-20 minutes, then transfer to serving plates. Dust with icing sugar and serve.