Preheat your oven to 300°F (150°C) and grease an 8-inch square baking pan to prevent sticking.

In a mixing bowl, combine the flour, 1 cup of sugar, egg, and baking powder. Mix until the ingredients are fully incorporated, creating a texture similar to coarse crumbs or cornmeal.

Peel, core, and slice the Granny Smith apples evenly, then toss them with ½ tablespoon of cinnamon to coat. Arrange the spiced apple slices evenly in the greased pan, ensuring a uniform layer.

Spread the prepared flour mixture evenly over the apples, covering them completely. In a small bowl, combine the remaining ¼ cup of sugar with 1 tablespoon of cinnamon, then sprinkle this mixture over the top of the flour layer. Drizzle the melted butter over the entire surface to enhance the crispness and flavor during baking.

Place the pan in the preheated oven and bake for approximately 1 hour, or until the topping turns a rich golden brown and the fruit beneath begins to bubble. Remove from the oven and let it cool slightly before serving.

Serve warm for the best flavor, and pair with a scoop of vanilla ice cream or a dollop of whipped cream if desired.