In a small bowl, whisk a tablespoon of water with the cornstarch and set it aside. In a medium saucepan, combine 1/2 lb. blueberries, sugar and 1 tablespoon water. Bring to a boil.
When blueberries reach a boil, reduce heat and simmer, stirring, until blueberries pop and mixture begins to thicken – about 3 minutes.
Add cornstarch mixture and Limoncello. Sub lemon juice if you don't have Limoncello (I ended up adding about 2 tbsp.) to thickened blueberries, stirring constantly. Simmer 30 seconds, stirring constantly. Fold in remaining blueberries. Let sit at room temperature until set, at least 1 hour. I refrigerated mine and used them the next day to fill my pie.
Food Processor Method: Put flour and salt in bowl of machine. Cut butter and vegetable shortening into flour. Process a few seconds until mixture resembles coarse meal.
Drop by drop add the sourdough starter, processing very briefly.
The whole process would take 20 to 30 seconds. (I had orginally added 1/4 cup sourdough starter. When I put on my counter to pat into discs, I noticed it needed a little more sourdough starter and added about 1 to 2 more tbsp.
Wrap and chill the pastry for at least 1 hour.
Preheat oven to 375°F with a foil-lined large baking sheet on middle rack.
Lightly flour a pastry board, marble counter, or kitchen counter. Roll first disc between parchment paper or plastic wrap (or 1/2 and 1/2 like I did here). Using pie plate as a guide, measure rolled-out pastry -- it should be slightly larger than the pie plate and 1/8-inch thick. Roll pastry in one direction only, turning pastry continually to prevent it from sticking to the surface.
Fold rolled pastry circle in half so you can lift it more easily. Unfold, gently fitting the pastry into the pie plate, allowing pastry to hang evenly over the edge. Prick the bottom of the pie crust with a fork. Add in your filling.
Roll out 2nd dough disk the same way you rolled out the first disc. Cut out a small vent circle in the middle of the pie and gently cut some ventilation slits (I made 4 with this one).
Brush the crust with an egg wash and sprinkle on some turbinado (or regular)sugar.
I bake my fruit pies over a baking tray lined with aluminum foil as the juices sometimes like to escape. Bake at 375 until crust is golden brown and juices bubble, 50 minutes–1 hour. Transfer to a wire rack to cool.