Preheat oven to 400°. In a small bowl, combine the cherries, nectarines, apricots, sugar, cornstarch, 2 tablespoons flour and cinnamon; set aside.
In another bowl, combine salt and remaining flour; cut in 3/4 cup butter until crumbly. Gradually add ice water, tossing with a fork until dough forms a ball. Divide dough into two portions so that one is slightly larger than the other. Roll out larger portion to fit a 9-in. pie plate; transfer pastry to pie plate. Add filling; dot with remaining butter.
Roll out remaining pastry; make a lattice crust. Trim, seal and flute edges. In a small bowl, whisk egg yolk and water; brush over lattice top.
Bake 45-50 minutes or until filling is bubbly and crust is golden brown. Cover edges with foil during the last 15 minutes to prevent overbrowning if necessary. Cool on a wire rack.