Prep: Preheat your oven to 350℉. Spray a 9x13 pan with nonstick spray and line with parchment paper, leaving enough overhang on the ends so you can lift the bars out for easy slicing later.
Prep the Apple Filling: In a medium bowl, toss together the apples with all the apple filling ingredients. Stir gently with a silicone spatula so as not to break up the apple slices. Make sure everything is well mixed and set aside.
5 medium apples, sliced between 1/8" and 1/4" thick, 1 tbsp lemon juice, 3 tbsp all-purpose flour , 1/3 cup light brown sugar, packed, 1 tbsp cinnamon, 3/8 tsp nutmeg, 1/4 tsp allspice, 1/4 tsp ground cloves, pinch of salt
Make the Crust/Topping: Melt the butter in a large bowl. Stir in the remaining bar ingredients.
1 and 1/2 cups salted butter, melted, 3 cups all-purpose flour, spooned & leveled or weighed out , 2 cups old-fashioned whole rolled oats, 1 and 1/2 cups light brown sugar, packed, 1 and 1/2 tsp baking soda, 1 tsp cinnamon, 1/2 tsp salt
Assemble: Reserve 2 cups (about 330 grams) of the crust mixture for the top of the bars. Press the rest of the mixture into your prepared pan. Give the apples another good stir, then spoon them over the base in an even layer, leaving the excess liquid behind in the bowl. Sprinkle the remaining crust mixture on top.
Bake: Bake the bars for 38 to 45 minutes. The topping will be golden and the apples will feel tender when you pierce through the topping and into the apple layer with a fork. Make the caramel while the bars bake. See next step. Let the bars cool on a wire rack on your kitchen counter for about 1-2 hours before slicing.
Make the Salted Caramel Sauce. Make the salted caramel sauce according to my salted caramel recipe here. This post gives in depth directions and step-by-step photos! 1 cup granulated sugar , 6 tbsp salted butter, cubed, 1/2 cup + 1 tbsp heavy cream, pinch of fine sea salt
Serve & Store: When ready to serve, slice the bars and drizzle with salted caramel as desired. Store bars in an airtight container in the fridge for 3-4 days (I recommend refrigerating whether or not they have the caramel on top). Any extra caramel should also be stored in an airtight container or jar in the fridge. I have tons of other recipes you can use the extra on!
Make-Ahead Tips: Caramel can be made up to 3 days ahead and refrigerated until ready to use. Microwave for 20-40 seconds to loosen it back up. Bars can be made up to 1 day ahead. Let cool at room temperature, then refrigerate until ready to serve. They're delicious warm, at room temperature, or cold!