Preheat oven to 450°. Whisk together sugar, flour and nutmeg; set aside. On a lightly floured surface, roll one-third of pie dough to a 1/8-in.-thick circle; cut into 2x1-in. strips. Layer a deep 12-in. enamel-coated cast-iron skillet or ovenproof casserole with half the strips; sprinkle with half the sugar mixture. Dot with half the butter. Repeat sugar and butter layers.
Roll remaining two-thirds of pie dough to a 1/8-in.-thick circle. Place over filling, pressing against sides of skillet or casserole. Cut a slit in top. Add vinegar to hot water; slowly pour vinegar mixture through slit. Liquid may bubble up through crust; this is normal. To catch spills, line an oven rack with foil.
Bake until crust is golden brown, about 1 hour. Cover edge loosely with foil during the last 15-20 minutes if needed to prevent overbrowning. Remove foil. Cool on a wire rack.