Preheat the Oven and Prepare the Pan:

• Preheat your oven to 350°F (175°C).

• Line a 9×9-inch baking pan with parchment paper or grease with butter or cooking spray to prevent sticking.

Make the Apple Filling:

• Peel, core, and slice the apples into thin pieces.

• In a medium bowl, mix the sliced apples, sugar, lemon juice, cinnamon, and cornstarch until well coated. Set aside.

Make the Crust and Topping:

• In a large bowl, combine flour, oats, sugar, baking powder, cinnamon, and salt. Stir until mixed.

• Add the melted butter and stir until the mixture forms a crumbly texture.

• Press about two-thirds of this mixture into the bottom of the prepared pan to form a crust.

• Set the remaining crumble mixture aside for the topping.

Assemble the Bars:

• Spread the apple mixture evenly over the pressed crust.

• Sprinkle the remaining crumble mixture on top of the apples.

Bake the Bars:

• Bake in the preheated oven for 40-45 minutes, or until the topping is golden brown and the apple filling is bubbling.

• If the topping starts to brown too quickly, cover the pan loosely with aluminum foil for the last 10 minutes.

Cool and Serve:

• Allow the bars to cool in the pan for at least 20 minutes before cutting them into squares.

• For the best results, let them cool completely before serving. Alternatively, serve warm with a scoop of vanilla ice cream!