2½ c all-purpose flour
1 t fine sea salt
1 t sugar
1 c (2 sticks) chilled unsalted butter, cut into ½” cubes
½ c sugar
2 T cornstarch
½ t ground cinnamon
½ t ground nutmeg
Pinch of fine sea salt
2½ lbs Golden Delicious apples (about 5 large), peeled, halved, cored, cut into ¼”-thick slices (about 7 cups)
2 T fresh lemon juice
1 large egg
2 T raw sugar
2 T pure maple syrup or agave syrup
Place flour, salt, and sugar in a food processor; pulse to blend. Add butter; pulse just until coarse meal forms. Add ¼ cup ice water; pulse until dough forms clumps, adding more ice water by teaspoonfuls if dough is dry. Gather dough into a ball; flatten into a disk. Wrap dough in plastic and chill 1 hour. (Note: Crust can be made 1 day ahead. Keep chilled. Allow to stand at room temperature for 15 minutes to soften slightly before rolling out.)
Preheat oven to 400°F. Place a large sheet of parchment paper on a work surface. Roll out dough disk on parchment paper to 15″ round (some of dough will extend over edges of paper). Whisk sugar, cornstarch, cinnamon, nutmeg, and salt in a large bowl. Add apples and lemon juice to bowl with sugar mixture; toss to coat apples evenly. Transfer apples to crust, mounding in center and leaving a 3″ plain border. Scrape out any juices from bowl and drizzle over apples.
Fold crust edges up over outer edges of filling, crimping dough and folding and pleating as needed to fit. Slide crostata and parchment onto a large baking sheet. Crack egg into a small bowl. Using a fork, beat egg just to blend. Brush crust edges with beaten egg, then sprinkle crust with raw sugar.
Place crostata in oven and bake until juices in center are thick and bubbling, about 1 hour. Let cool for 5 minutes. Run a long, thin knife or offset spatula around edges of crostata to loosen from paper and to prevent it from sticking to the paper. Transfer baking sheet with crostata to a wire rack. Brush apples generously with maple syrup, or drizzle with agave syrup. Let crostata cool. Serve warm with Brown Butter Ice Cream.