Prep the Oven and Apples: Preheat your oven to 350°F / 175°C.
Arrange the peeled, cored, and thinly sliced apples in an 8x8-inch (20x20 cm) baking dish.
Pour the water over the apples, then sprinkle with 2 tablespoons (30 ml / 1 fl oz) of brown sugar and ½ teaspoon of cinnamon. Gently toss to coat the slices evenly.
Mix the Topping: In a separate mixing bowl, whisk together the whole wheat pastry flour, ½ cup of brown sugar, 1 teaspoon (5 ml / 0.2 fl oz) of cinnamon, and the salt.
Cut in the Butter: Add the cold, cubed butter to the flour mixture.
Using a pastry cutter or your fingertips, work the butter into the dry until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
Assemble and Bake: Sprinkle the topping mixture evenly over the prepared apples.
Bake for 30 to 40 minutes, or until the apple filling is bubbly and tender, and the topping is a beautiful golden brown.
Cool and Serve: Let the apple crisp cool on a wire rack for at least 15 minutes. The topping will become crispier as it cools.
Serve warm, either on its own or with a generous scoop of vanilla ice cream.