Preheat oven to 350 degrees F. For Port wine reduction: Combine the port with the mirepoix and reduce by 2/3 to a syrup consistency, about 6 to 8 minutes.
For stuffed pears: Combine the blue cheese and walnuts together. Stuff each pear with 1/4 of the mixture. Place a pear in the center of the halved puff pastry sheet and wrap like a bundle, trimming any excess, thus leaving the shape of the pear evident. Brush each pear with the egg wash and bake until golden, about 8 to 10 minutes.
To assemble, place the pear in the center of the plate, drizzle with the Port wine reduction, sprinkle with the walnuts and chives.