Cut an X in bottom of each peach, then blanch peaches in batches in boiling water 15 seconds.
Transfer with a slotted spoon to an ice bath to stop cooking. Peel peaches and cut into 1-inch-thick wedges.
Toss peaches well with cornstarch, flour, lemon juice, cinnamon, and salt in a large bowl.
Put a foil-lined large baking sheet in lower third of oven and preheat oven to 425°F.
Bring 1/2 cup sugar, honey, and water to a boil in a 1 1/2-to 2-quart heavy saucepan over medium-high heat, stirring until sugar has dissolved, then wash down any sugar crystals from side of pan with a pastry brush dipped in cold water. Boil without stirring, swirling pan occasionally so caramel colors evenly, until dark amber, about 5 minutes.
Remove from heat and add butter, swirling pan until butter is melted.
Pour over fruit and toss (caramel may harden slightly but will melt in oven).
Roll out 1 piece of dough (keep remaining piece chilled) into a 13-inch round on a lightly floured surface with a lightly floured rolling pin. Fit into a 9-inch pie plate. Trim excess dough, leaving a 1/2-inch overhang. Chill shell while rolling out remaining dough.
Roll out remaining piece of dough into an 11-inch round on a lightly floured surface with a lightly floured rolling pin.
Transfer filling to pie shell, mounding it. Cover pie with pastry round. Trim with kitchen shears, leaving a 1/2-inch overhang. Press edges together, then crimp decoratively.
Brush top all over with some of milk, then sprinkle with remaining tablespoon sugar.
Cut 3 steam vents in top crust with a paring knife.
Bake pie on hot baking sheet 20 minutes. Reduce oven temperature to 375°F. Continue to bake until crust is golden-brown and filling is bubbling, about 50 minutes more. Cool pie to room temperature, 3 to 4 hours.
