• Preheat your oven to 350°F, ensuring the rack is positioned in the center. Line an 8x8 baking pan with foil or parchment paper, greasing it lightly, and set it aside for later use.

Crust and topping:

• Using a hand mixer or a stand mixer fitted with the paddle attachment, combine granulated sugar, brown sugar, flour, baking powder, and salt until well mixed.
• Add the cubed butter and vanilla extract, and beat until the butter is broken into small, irregular pieces. If needed, use your fingers to rub the butter into the flour mixture.
• Once the mixture is crumbly and the butter resembles small pebbles, transfer it to the refrigerator while you prepare the filling.

Filling:

• In another bowl, mix together all the ingredients for the apple filling. Stir until everything is evenly combined.

Assembly:

• Scoop 2 cups (loosely measured, not tightly packed) of the crust and topping mixture into your baking dish. Use the back of a measuring cup to firmly press it into an even layer, creating the crust. Set aside any remaining crumb mixture for later use.
• Next, add the sliced apples on top of the crust, arranging them in tight layers and overlapping the pieces for even coverage.
• In a separate bowl, mix together ⅓ cup of oats and ¼ teaspoon of cinnamon with the reserved crumb mixture. Sprinkle this topping evenly over the apples, making sure to press some of it together to create clumps for added texture.
• Cover the dish with foil and bake for 30 minutes. After this time, remove the foil and continue baking for an additional 25-30 minutes, or until the topping turns a light golden brown and the apples are tender (you can check tenderness by inserting a sharp knife). Once done, transfer the pan to a wire rack to cool.
• For serving, drizzle caramel sauce over the top. These bars can be enjoyed warm, at room temperature, or chilled. For a delicious twist, serve them with ice cream and an extra drizzle of caramel sauce. Note that chilling the bars will help them cut more neatly.