Preheat the oven to 350F. Grease and line an 8x8” square baking pan with parchment paper; set aside.

In a medium bowl, add the softened butter and sugar. Beat for ~1min, until light and fluffy. Add in the sourdough discard, and mix until incorporated. Add the vanilla, and mix again. Then, add the salt and flour, and mix until soft chunks of dough form.

Pour the dough into the prepared baking pan, and use your fingers to press into an even layer on the bottom of the pan. Prick the crust with a fork, and bake at 350F for 20-25 minutes, until the edges start to brown and it is baked through. Remove from the oven and set aside to cool.

In a saucepan over medium heat, add the butter, brown sugar, spices, water, and lemon juice. Mix until the butter is melted. Add the apples and mix. Cover and cook for ~10 minutes, until the apples are softened.

Then, add the cornstarch/water mixture, and mix until well combined and the apple mixture is thickened. Set aside and cool.

In a medium bowl, mix together all of the ingredients until well combined and the mixture is crumbly. Set aside.

Evenly and tightly layer the apples on top of the shortbread crust. Then, sprinkle the apple layer with the crumble.

Bake at 350F for 30-35 minutes, or until golden brown.

Remove from the oven and allow to cool for at least 20 minutes.

While cooling, make the salted caramel by mixing together all of the ingredients in a medium bowl. Then, drizzle the bars with the salted caramel.

Slice into 16 bars, and serve warm, at room temperature, or chilled with a scoop of vanilla ice cream, if desired.