In a food processor, pulse flour and salt to combine. Add butter and pulse until the size of small peas. Add 6 tablespoons water and pulse 15 times. If dough is still dry, add more water, 1 tablespoon at a time, until dough just comes together. Divide dough in half, shape into discs, wrap in plastic wrap, and refrigerate at least 1 hour.
Preheat oven to 425°F. In a large bowl, combine cherries, stevia, cornstarch, and lemon juice. On a lightly floured surface, roll half the dough into a 12” circle. Transfer to a 9” pie pan, pressing gently into the corners. Trim edges so the dough hangs ¼” over the sides. Refrigerate.
Roll out the rest of the dough as above, and cut into ¾” wide strips. On a lightly floured cookie sheet, place half the dough strips ½” apart, then weave the remaining strips through them in a perpendicular, alternating over, under pattern. Remove crust from refrigerator and pour filling into it. Slide lattice off the cookie sheet directly on top of the pie. Trim lattice strips, leaving a ¼” overhang. Tuck ends of the strips under the edge of the bottom crust, then crimp the edge. Brush top of the pie with milk and sprinkle with sugar, if desired. Bake 30 minutes, then lower heat to 350°F and bake until the juices are thick and bubbling, about 25-30 minutes. Cool on a rack.