Instructions

for the filling

Combine peaches, sugar, and salt in Dutch oven. Cook peach mixture over medium-high heat, stirring occasionally, until juice is reduced to thick syrup and spatula dragged through mixture leaves trail that doesn't fill in immediately, 25 to 30 minutes. Transfer to large bowl and refrigerate until completely cooled, at least 2 hours. (Filling can be refrigerated for up to 3 days.)

for the pie dough

Meanwhile, mix ice water and sour cream in bowl. Process flour, granulated sugar, and salt in food processor until combined, about 5 seconds. Scatter butter over top and pulse until butter pieces are no larger than peas, about 10 pulses.
Add half of sour cream mixture to flour mixture and pulse until incorporated, about 4 pulses. Scrape down sides of bowl; add remaining sour cream mixture; and pulse until dough forms large clumps and no dry flour remains, about 6 pulses.
Transfer dough to counter and knead briefly until it comes together. Divide dough in half. Form 1 half into 5-inch disk and second half into 5-inch square, pressing any cracked edges back together. Wrap separately in plastic wrap and refrigerate for 1 hour. (Wrapped dough can be refrigerated for up to 2 days or frozen for up to 1 month. If frozen, let dough thaw completely on counter before rolling.)
Adjust oven rack to lowest position and heat oven to 375 degrees. Let chilled dough sit on counter to soften slightly before rolling, about 10 minutes. Roll dough disk into 13-inch circle on lightly floured counter. Loosely roll dough around rolling pin and gently unroll it onto 9-inch pie plate, letting excess dough hang over edge. Ease dough into plate by gently lifting edge of dough with your hand while pressing into plate bottom with your other hand.
Wrap dough-lined plate loosely in plastic and refrigerate until dough is firm, about 30 minutes. Roll dough square into 13 by 11-inch rectangle on lightly floured counter, with long side parallel to counter's edge. Using pizza cutter or chef's knife, trim ½ inch of dough from short sides of rectangle (sides perpendicular to counter's edge) to create clean edges. Cut six 2-inch-wide strips of dough perpendicular to counter's edge. Transfer strips to parchment paper–lined baking sheet, cover with plastic, and refrigerate for 30 minutes.
Stir lemon juice and cornstarch together in small bowl, add to cooled peach mixture, and stir to combine. Transfer peach mixture to dough-lined pie plate, spread into even layer, and dot with butter.
To make lattice, lay 1 dough strip across center of pie, parallel to counter's edge. Lay second strip across center of pie to form cross. Lay 2 strips across pie, parallel to counter's edge, on either side of middle parallel strip, about ¾ inch away from middle strip.
Fold back left side of middle parallel strip. Lay 1 strip across left side of pie, perpendicular to counter's edge, about ¾ inch away from middle perpendicular strip. Unfold middle parallel strip to cover. Repeat with right side of middle parallel strip and remaining dough strip.
Shift strips as needed so they are evenly spaced over top of pie. Pinch edges of lattice strips and bottom crust together firmly. Trim overhang to ½ inch beyond lip of plate. Tuck overhang under itself; folded edge should be flush with edge of plate. Crimp dough evenly around edge of plate using your fingers.
Brush lattice top and crimped edge with egg and sprinkle with turbinado sugar. Set pie on parchment-lined baking sheet. Bake until well browned and juices bubble around outer edge between lattice strips, about 1 hour, rotating sheet halfway through baking. Let cool on wire rack for at least 6 hours. Slice and serve.