Preheat oven to 350℉. Line a 8x8 inch baking tray with parchment paper.

Add the butter to a bowl and melt in microwave. Prepare other ingredients while the butter cools slightly.

Add the flour, oats, brown sugar, cinnamon and salt. Mix to combine into a crumbly topping. Place in the refrigerator while preparing the remaining ingredients.

In another bowl melt butter and add brown sugar, vanilla, flour, oats and salt. Mix to combine and place mixture into the prepared baking pan. Press into a thin layer getting the crust into the corners of the pan.

Bake in preheated oven for 12-15 minutes.

While the crust is baking, peel and thinly slice the apples about ¼ inch thick.

Place the apples in a bowl and toss with sugar, flour, cinnamon, nutmeg and allspice.

Once the crust is removed from the oven top with the cinnamon sugar apples, then add the crumble layer to the top to cover the apples.

Bake in the preheated oven for 35-40 minutes or until the apples are soft when poked with a fork. If the crumble topping begins to brown too much cover with a piece of aluminum foil.

When bars are finished baking allow to cool at room temperature for an hour and then transfer to the refrigerator to finish cooling, they are much easier to cut when cooled!

Add the sugar to a stainless steel saucepan (do not use nonstick). Heat the sugar over medium heat and use a wooden spoon to stir. After several minutes the sugar will begin to clump and melt. Continue to stir until the sugar has completely melted and turned a light amber color.

When the sugar has melted completely, turn the heat down low. Add the butter and stir vigorously to mix the butter into the sugar. It may not fully incorporate and a little separation is normal.

Next, remove the pan from the heat and slowly whisk in the heavy cream a little at a time. Expect to see a little bubbling when the cream is added. Continue to stir until the caramel sauce comes together. Stir in the sea salt and vanilla. This will thicken as it cools. It will keep in a jar in the refrigerator for up to 1 month.

Drizzle over apple bars and enjoy cold, room temperature or warmed with vanilla ice cream.