Preheat oven to 425 degrees F (220 degrees C). Place cherries, nectarines and apricots into a colander to drain off any excess liquid.
To Make Dough: In a medium bowl, combine flour and salt. Cut 3/4 cup of butter into flour mixture until it resembles coarse crumbs. Pour in one tablespoon of water at a time until the dough sticks together. Add additional water if necessary. Divide dough into two parts. Roll out one half toa circle 1/8 of an inch thick, then place in a 9 inch pie pan. Roll out the other half of the dough and cut into long strips about 1/2 inch wide. Set aside.
To Make Filling: Place the drained fruit mixture into a medium bowl, Stir in the sugar, cinnamon, cornstarch and flour; pour into the prepared pie pan. Dot with the remaining two tablespoons of butter. Arrange the pastry strips into a lattice top and crimp edges. In a small bowl, whisk together the egg yolk and teaspoon of water, and use a pastry brush to coat just the lattice strips--not the edges.
Bake in the preheated oven and bake for 25 minutes, until the crust begins to brown. Reduce the heat to 350 degrees F (175 degrees C) and bake for an additional 20 to 25 minutes. Remove from oven and let cool a bit before serving.
