Preheat oven to 425°F. Place a rimmed baking sheet on the center rack while the oven heats. If using frozen crusts, allow to thaw.

Peel, core, and slice apples into 1/4-inch-thick slices. In a large bowl, toss apples with lemon juice, granulated sugar, and brown sugar. Let stand for 30–45 minutes, stirring once or twice, until the apples have released a generous amount of juice.

Drain juices from apples into a small saucepan; reserve the apples in the bowl. Whisk gochujang, cornstarch, grated ginger, coriander, orange zest, vanilla, melted butter, and salt into juices until smooth. Place saucepan over medium heat and cook, stirring constantly, until mixture thickens and gochujang is fully dissolved, about 2–3 minutes.

Pour warm glaze over apples and gently toss until every slice is evenly coated. Transfer filling to a prepared 9-inch piecrust, arranging apples evenly and scraping any remaining glaze over the top. If using ready-made crust, remove the second crust from the pan it came in; use it to cover the pie. Otherwise, cover with prepared top or lattice crust. Trim and crimp edges. If using a full crust, cut several vents in the top crust. Brush with egg wash and sprinkle with coarse sugar, if desired.

Place pie on the preheated baking sheet and bake for 20 minutes. Reduce the oven temperature to 375°F and continue baking until the crust is deeply golden and the filling is bubbling through the vents or lattice, 35–45 minutes more. If the edges begin to brown too quickly, cover them loosely with foil.

Transfer pie to a wire rack and let cool for at least 3 hours before slicing. The filling will continue to set as it cools, allowing ingredients to meld fully and making slicing easier.

Pie can safely stay at room temperature for up to 2 days, loosely covered with foil or a cake dome. After 2 days, cover and refrigerate.