In a large bowl, stir together the flour, salt, and sugar. Place the ice in the water and set aside.
Cut in the cold butter with a pastry cutter or by hand, rubbing the pieces of butter between your thumb, index, and middle fingers. Once the pieces are no longer lager than about a peanut, begin to flatten the pieces of butter in sheets between your palms. Be careful not to over-work the butter or let it get too warm.
Working with only a couple tablespoons at a time, add in about 6 to 8 tablespoons of the water along with the vinegar. Stir together using a wooden spoon or even just a clean hand in the bowl. The dough should appear fairly shaggy and not sticky. Once you can squeeze a few pieces together and they hold, the dough is done being mixed. Do not over-mix.
Divide the dough into half and shape each piece into a disk. Wrap in plastic and refrigerate for at least a couple of hours, or overnight (preferably).
Once ready, bring one disc out of the refrigerator and allow to rest for about 10 minutes. Liberally flour the work surface and begin to roll out the dough, working from the center out – rotating the dough after each roll. Roll the dough until about ¼ inch thick and about 12 to 13 inches in diameter.
Gently roll the dough around the rolling pin and transfer to a 8 or 9 inch pie tin. Fit the dough into the bottom of the tin and up the sides, allowing for about an inch of overhang. Trim with kitchen sheers and place back in the refrigerator.
Meanwhile, make the pear filling (recipe to follow).
For the lattice top, repeat step 5 Using a ruler and pastry wheel or sharp paring knife, cut dough into 1 to 2-inch wide strips. The centre strips should be slightly longer than the diameter of the pie pan. You’ll need about 6 to 10 strips to create the lattice top, depending on desired width and spacing in between. Place the strips on a baking sheet and chill in the refrigerator.
Fill the chilled pie crust by layering in the pear slices fairly tightly, leaving the juices behind. Top with about ¾ cup butterscotch sauce (recipe to follow).
Weave the strips together to create a lattice pattern over the top of the butterscotch, trying not to get too much butterscotch on the top of the pie. Fold the bottom layer of dough up and over the top of the lattice. Pinch to seal. Crimp the edges together using the tines of a fork and dock the crust to the pan.
Return the pie back to refrigerator for at least 15 minutes. Meanwhile, pre-heat oven to 400 degrees.
Just before heading into the over, create an egg wash by whisking together a whole egg and a splash of milk. Brush the egg wash over the entire top of the crust and sprinkle with turbinado sugar and salt flakes.
Place pie on a baking sheet and bake for about 40 to 45 minutes, or until golden brown. If the top begins to brown too quickly, cover with foil.
Allow the baked pie to completely cool before slicing and serving.