Slice the unsalted butter into thin pieces ahead of time and keep it in the refrigerator to stay cold. Mix all-purpose flour with granulated sugar and salt until combined. Add the chilled butter and coat with flour.
Add ice water gradually, mixing each time to allow the flour to absorb the water evenly, until no large patches of dry flour remain in the bowl.
Transfer the dough onto a work surface, pressing and folding repeatedly until it comes together. Wrap in plastic wrap and freeze for 20 minutes.
Roll the dough into a rectangle about 40 cm long and 15 cm wide. Fold it into thirds along the long side. Rotate 90 degrees, roll again into the same rectangle, and fold into thirds again.
Roll lightly to seal the layers together. Divide into two portions, wrap in plastic wrap, and refrigerate for at least 2 hours before use.
Preheat the oven to 220°C (425°F). Place a baking sheet inside on the lower-middle rack to preheat. Prepare a 9-inch pie pan, 3 cm deep, preferably metal.
Take one portion of dough and roll it into a circle at least 12 inches wide. Place it into the pie pan, lifting the edges so it drapes into the bottom. Press gently into the bottom and sides. Refrigerate.
Roll the other portion into a rectangle at least 12 inches long and 10 inches wide. Trim uneven edges. Slice lengthwise into 8 even strips. Chill again in the refrigerator.
Peel and slice or dice the apples. Mix with lemon juice, granulated sugar, and cinnamon powder. Add cornstarch and stir to coat evenly. Transfer into the prepared pie pan, arranging neatly.
Take four strips of dough and place them parallel across the top. Fold back alternating strips (1 and 3, then 2 and 4) to weave the remaining four strips crosswise, creating a lattice.
Seal the edges of the crusts by pressing them together. Trim excess dough, leaving about 2–3 cm overhang. Fold inward and press gently. Crimp with fingers into a wavy edge for a tight seal.
Beat the egg and brush evenly over the top crust. Sprinkle with coarse sugar. Place the pie in the preheated oven and bake for 20 minutes. Reduce the temperature to 190°C (375°F) and bake another 45 minutes to 1 hour, until golden brown and the juices at the edges are bubbling.
Cool the pie for 3–4 hours until room temperature before serving.
Keep the sliced butter cold before using to prevent it from melting too quickly during mixing. Maintaining solid, cold butter is the key to a flaky crust.
The pie dough can be made 2–3 days in advance. Wrap tightly in plastic wrap and refrigerate.
Using a preheated baking sheet helps catch overflowing juices and ensures the pie bottom bakes crisp.
For a deeper pie pan, add an extra pound of apples and adjust the other filling ingredients proportionally.
The variety of apples affects the final flavor, aroma, and texture of the pie. Choose according to preference. See this blog for reference.
Do not cut the pie immediately after baking. During cooling, apple pectin and gelatinized cornstarch thicken the juices, making the pie easier to slice.