1 Make the dough: To make the dough, place flour, sugar, and salt into a food processor and pulse a couple of times.
Add half of the butter and pulse 8 1-second pulses. Add the rest of the butter and pulse several more times, until the largest piece of butter is no larger than a pea.
Add 2 Tbsp of very cold water to the dough. Pulse a couple of times. Continue to add icy water, a teaspoon at a time (no more than 3 teaspoons) until the dough just holds together when you pinch some with your fingers.
Empty the food processor bowl onto a clean surface. Gather up the dough into your hands and form a ball. Flatten into a disk and wrap tightly with plastic wrap. Chill for at least 1 hour.
2 Peel, slice apples, toss with lemon: As the dough is chilling, peel, core, and slice the apples into 1/4-inch to 1/2-inch slices. Place in a large bowl and sprinkle with the lemon juice and lemon zest. Toss the apple slices around in the bowl so that they are all a little coated with the lemon juice.
3 Whisk sugar, cornstarch, spices, then toss with apples: In a bowl, whisk together the sugar, cornstarch, ground cinnamon, ground nutmeg, and salt. Sprinkle over the apple slices and gently mix so that the apple slices are all well coated with the sugar mixture.
4 Preheat oven to 400°F (205°C).
5 Roll out dough: Remove dough from refrigerator and let sit 5 to 10 minutes before rolling out. Place on a lightly floured clean surface and roll out to a 14 inch (35 cm) round. (The dough round will be on the thin side.) Pro-tips: don't let the dough stick to the table. If it starts to stick, sprinkle the surface with more flour. If the dough gets too soft to work with, chill in the refrigerator for a few minutes.
6 Mound apples on dough round: Gently transfer to a parchment lined rimmed baking sheet. Mound the apples in the center of the dough round, allowing for a 2 1/2 to 3 inch (6 to 8 cm) margin around the edges. Gently lift up and drape the edges over the apples.
7 Brush with egg wash, sprinkle with sugar, dot with butter: Whisk together the egg white and cream. Use a pastry brush to brush over the exposed areas of the crust. Sprinkle the top of the crostata with sugar. Dot the exposed apples with butter.
8 Bake: Bake at 400°F (205°C) for 45 minutes to an hour, checking after 30 minutes or so. If the apples start to brown too much, tent them with foil.
9 Cool: Remove from oven and let cool on a rack for 30 minutes to an hour before serving.
10 Make whipped cream: To whip the cream, place the cream, powdered sugar, and vanilla extract in a mixing bowl (sometimes I like to freeze the empty bowl so it stays colder when whipping the cream). Use a hand mixer to whip until you have soft peaks. Chill until ready to serve.
Serve the apple crostata with whipped cream or vanilla ice cream.