Step 1

In a food processor, pulse the flour, butter, and salt until the mixture forms small pebbles. Add the water, 1 tablespoon at a time, pulsing a couple of times after each tablespoon, until the dough just starts to gather into a large ball.

Step 2

On a work surface, form the dough into a disk, wrap in plastic, and place in the refrigerator for 30 minutes.

Step 3

Heat oven to 400°F. Peel and slice the apples ¼ inch thick. Transfer to a large bowl. Add ½ cup of the brown sugar, 2 tablespoons of the flour, 1 teaspoon of the cinnamon, ½ teaspoon of the nutmeg, and ¼ teaspoon of the salt. Toss until well combined.

Step 4

On a lightly floured surface, roll out the dough to a circle about 12 inches across. Arrange the dough in a 9- or 10-inch pie pan with at least 1-inch-high sides (higher is better, but use what you have). Crimp the edges if you're feeling fancy. Place the pie plate on a large cookie sheet (trust me on this one) and pile the apple mixture into the pan—you will have a fairly tall mountain of apples.

Step 5

In a medium bowl, combine the walnuts, oats, butter, and the remaining ½ cup of the flour, ½ cup of the brown sugar, ½ teaspoon of the cinnamon, ¼ teaspoon of the nutmeg, and pinch of the salt. Cover the apples with the topping as completely as possible. Sprinkle the topping with the turbinado sugar, if using.

Step 6

Place the cookie sheet with the pie on top into the oven and bake for 10 minutes. Reduce the oven temperature to 350°F and continue to bake for 60 to 75 minutes, until the topping is well-browned. Let cool on a wire rack before serving.