• Lightly oil the bottom and sides of an 8 inch by 8 inch baking pan with pan spray or vegetable oil. Line the pan with parchment paper leaving "handles" to lift the apple bars out of the pan. Set aside.

Make the Crust and Topping:

• In a small sauce pot, add the butter and heat on low. Once melted, set aside and allow it to cool.
• In a medium mixing bowl, whisk the flour, cane sugar, 1/4 cup brown sugar, 1/2 teaspoon of cinnamon and salt.
• Make a well in the center of the dry ingredients and pour in the melted butter. Add the vanilla extract to the bowl. Use a wood spoon to pull the flour mixture into the center of the well, stirring and incorporating the flour into the butter. Stop mixing when no dry bits remain and the mixture is crumbly. This is your shortbread crust dough.
• Make the Streusel Topping: Transfer 3/4 cups (150 grams) of the crumbly shortbread dough to a small bowl. Add the remaining 1 tablespoon of brown sugar, 1/2 teaspoon of cinnamon and all the oats. Mix together using your hands. The topping should be crumbly. Set aside.
• Press in the Shortbread Crust: Knead the remaining shortbread dough a few times to bring the crumbles together, then transfer the dough to the prepared pan. Press the dough into the pan in an even layer. Use the bottom of a dry measuring cup or Mason jar to smooth and even the layer if needed.

  Place in the freezer for 15 minutes.
• Arrange a baking rack to the center of the oven. Preheat the oven to 350 Fahrenheit (180 Celcius).
• Bake the shortbread crust for 25-30 minutes or until darker golden around the edges and golden in the center. Set aside.

Cook the Apples:

• Meanwhile, place the thinly sliced apples in a Dutch oven or large stock pot. Add the maple syrup, 1 tablespoon of juice (cider or water), zest and juice of one lemon, vanilla, cinnamon, nutmeg and salt.
• Turn the heat to medium and gently stir the apples. Once you hear the ingredients bubbling, turn the heat to low and cook for about 10 minutes stirring occassionally. The apples will begin to cook down, become soft and release their juices.

  Once done, the apples should be just fork tender.

  Remove from heat and make a slurry of 1 tablespoon of juice or water with the cornstarch. Pour it into the apple mixture, return the pot to medium heat and bring to a simmer, stirring to coat the apples, for about 30 seconds or until the mixture thickens and the apples are glossy. Remove from heat and set aside.

Assemble and Bake the Apple Bars:

• Transfer the apples to the baked crust, gently spreading and pressing into one even layer - be sure to get the corners. Sprinkle the streusel topping over the apples in an even layer.

  Bake at 350 Fahrenheit (180 Celcius) for 30-35 minutes or until the top is golden and apples fragrant.
• Transfer the pan to a cooling rack and allow to cool completely in the pan (about one and a half to two hours).
• Lift the bars out of the pan using the parchment as handles. Use a serrated knife, cut the bars in one assertive downward motion, into 16 pieces.

To Store / Reheat:

• Store bars at room temperature for up to two days, or up to two weeks in the freezer. Thaw for about an hour before reheating.

  Reheat in a 350 Fahrenheit oven for about 10-15 minutes or until warmed through.