2) Line a baking sheet with parchment paper. Stir together the cornstarch and 1 1/2 tablespoons cold water in a small bowl.
3) Combine apples, pears and lemon juice in a large saucepan and add sugar. Cook over medium heat, stirring occasionally, until juices are released, about 10 minutes. Add cornstarch mixture; bring to a boil, stirring often. Remove from heat, add vanilla and let cool to room temperature.
4) Roll out pastry on a lightly floured surface to an 18 x 15" rectangle. Using a sharp knife, cut dough into 8 equal rectangles.
5) Place 1 pastry rectangle on a work surface at a time and brush edges with egg wash. Scoop about 3 tablespoons fruit mixture onto one side; fold dough over filling so the short ends meet, forming a packet. Crimp edges with a fork to seal. Using a sharp knife cut a few slits in top of pie to vent. Place on prepared baking sheet; repeat with remaining dough and filling.
6) Brush tops with egg wash, then sprinkle with raw sugar. Chill for 30 minutes. Bake pastries until tops and bottoms are golden brown, 30-40 minutes. Let cool for 10 minutes on baking sheet. Dust pies with powdered sugar if desired and serve with whipped cream or ice cream.