This recipe is delicious, though is time-consuming to assemble. It helps to break the recipe into two days: make the shortcake crust, then later make the entire cake. The shortcake is best eaten within two days, but keeps very well frozen in slices.
In the bowl of a food processor, pour in the flour, 1 cup sugar, baking powder, and 1 1/4 teaspoons salt, then pulse until combined. Cut the butter into cubes and add to the bowl, pulsing until the mixture resembles coarse crumbs. Add 2 eggs and the extracts. Pulse to bring the dough together so that it's moist but not sticky; if it doesn't come together, add a small amount of water and pulse more.
Turn out the dough to press it together. Use a food scale to weigh the dough and divide it in two. Wrap each piece with plastic wrap. Chill in fridge for at least 30 minutes, or up to a few days.
Assemble the shortcake
Preheat oven at 350-degrees. Let the dough stand at room temperature for about 10 minutes. Sprinkle flour on a flat surface and roll out one portion of dough to make a 13-inch square. Set the pan on top as a guide to cut an even 9x9 square.
Line pan with foil and apply nonstick spray. Place cut square inside. It's okay if it tears as its being moved--patch it with fingertips. Pat the leftover dough up the sides of the pan to completely cover, sealing the edges together along the bottom and at the corners. Chill pan during the next step.
Peel the apples and cut into quarter-inch slices, placing them in a large bowl. Add the lemon zest and 2 teaspoons of juice. Stir to coat apples. Add the cornstarch, cinnamon, remaining 3 Tablespoons sugar, and last bit of salt. Toss everything together, coating the apples. Spread the apples evenly across the bottom of the pan.
Roll out remaining dough to make a 10-inch square to completely cover the top of the apples. Press overlapping edges to seal together, trimming dough if needed. Lightly beat the remaining egg then brush it over the top crust. Use a fork to poke the crust all over to create vents. If desired, sprinkle turbinado sugar across the crust.
Bake until crust is golden brown, about 50 minutes to 1 hour. The apples should be tender if poked with a toothpick. Let cool in pan for at least an hour. Use foil to lift shortcake onto a cutting board for easy slicing.
Store cake in sealed container at room temperature for up to 2 days. It can also be cut into individual slices and frozen for later enjoyment.