Preheat your oven to 375°F (190°C). Lightly spray an 8 or 9-inch baking dish with nonstick cooking spray to prevent sticking, and set it aside while you prepare the filling and topping.

In a medium bowl, whisk together the all-purpose flour, packed brown sugar, baking powder, salt, and ground cinnamon until well combined. Pour in the melted unsalted butter and stir with a fork until the mixture forms coarse, crumbly clumps. I like to use my hands toward the end for perfectly sized crumbs.

In a large bowl, combine the peeled, cored, and chopped Granny Smith apples with granulated sugar (or brown sugar), lemon juice, cornstarch (or flour, as preferred), salt, and ground cinnamon. Stir everything together so the apples are well coated. For a brighter flavor, I always use fresh lemon juice here.

Spread the apple filling from Step 3 into an even layer in the prepared baking dish. Sprinkle the crumble topping from Step 2 evenly over the apples to fully cover the fruit.

Place the assembled apple crisp in the preheated oven. Bake for 35 to 45 minutes, or until the topping is golden brown and the fruit is bubbling. I sometimes place a baking sheet underneath in case any juices bubble over.

Allow the apple crisp to cool for about 15 minutes before serving. This rest time helps the filling set slightly, so each serving holds together nicely. For an extra treat, I love serving it warm with a scoop of vanilla ice cream on top!