1. Prepare the Apple Filling:
Peel, core, and slice the apples evenly. Place them in a 9×13-inch baking dish. Mix the white sugar, 1 tablespoon of flour, and cinnamon, then sprinkle the mixture evenly over the apples. Pour 3 tablespoons of water over the apples.

2. Make the Crisp Topping:
In a bowl, combine the quick-cooking oats, 1 cup of flour, brown sugar, baking powder, and baking soda. Add the melted butter and mix until the ingredients form a crumbly topping.

3. Assemble and Bake:
Preheat the oven to 350°F (175°C). Sprinkle the crumb topping evenly over the apples. Bake for about 45 minutes, or until the apple filling is bubbling and the topping is golden and crisp.

4. Cool and Serve:
Let the apple crisp cool slightly before serving. Serve warm, preferably with vanilla ice cream.