• Preheat oven to 350°F. Lightly grease a 9-inch square baking pan. Line the pan with piece of parchment paper so the excess hangs over the sides like a sling. Set aside.

Prepare the topping

• In a medium bowl combine the oats, flour, brown sugar, cinnamon, baking soda and salt. Add the melted butter and stir until combined. Refrigerate until needed.

Prepare the crust

• Beat the butter and sugar with an electric mixer until light and fluffy. Add the flour, salt and vanilla and mix until a soft dough forms. Press the dough evenly into the bottom of the prepared baking pan. Bake for 13 to 16 minutes or until the crust is just set but not brown.
• Set aside to cool while preparing the apples.

Prepare the apples

• Peel, core and slice the apples and place in a large bowl. Sprinkle the juice of 1 lemon over the apples and toss to coat.
• In a large skillet melt the butter and brown sugar over medium-high heat. Add the apples and cook stirring occasionally until softened. Stir in the apple cider, cinnamon, nutmeg and bourbon (if using) into the apple mixture and cook another 5 minutes or until the apples are caramelized, tender and the liquid is absorbed.

Assemble the apple bars

• Spread the apples evenly over the crust. Using a spoon break the topping into clumps and sprinkle over the apples. Lightly press the topping down to make an even layer. Bake for 40 to 45 minutes or until the topping is golden brown. Cool completely then cut into 9 bars. You can also cut each square diagonally into wedges to create 18 bars.
• Stir the bourbon into the caramel sauce if using. Drizzle the caramel over the bars and serve. Top with a scoop of ice cream if desired, and more caramel sauce of course!