Start by heating your oven to 350 degrees Fahrenheit and prepare a 9x13 inch pan with nonstick spray and parchment paper, leaving extra on the edges for easy removal later.
In a bowl, combine the sliced apples with lemon juice, flour, brown sugar, cinnamon, nutmeg, allspice, cloves, and a pinch of salt. Gently toss so the apple slices stay intact and the spices distribute evenly.
Pour melted butter into a large mixing bowl, then add the flour, rolled oats, brown sugar, baking soda, cinnamon, and salt. Mix everything until well combined.
Set aside about 2 cups of this oat mixture for the topping and press the remainder firmly into the bottom of the prepared pan to form the crust.
Give the spiced apple filling another gentle stir, then spread it evenly over the crust, leaving any excess liquid behind in the bowl.
Sprinkle the reserved oat mixture evenly over the apples as a crumble topping.
Bake the assembled bars for 38 to 45 minutes until the top turns golden and the apples are tender when tested with a fork.
While baking, prepare the salted caramel sauce by melting sugar in a saucepan until amber colored, then whisk in the cubed butter until smooth.
Slowly add the heavy cream and a pinch of fine sea salt, stirring constantly until the sauce is velvety and glossy.
Allow the bars to cool completely on a wire rack for 1 to 2 hours before lifting them out using the parchment paper overhang for easier slicing.
When ready to serve, cut the bars into desired portions and drizzle generously with the homemade salted caramel sauce.
Store any leftover bars in an airtight container in the refrigerator for up to 3 to 4 days, and keep extra caramel sauce refrigerated as well, reheating gently before use.
