Prepare the cake mixes according to the package direction and bake in 8- or 9-inch cake pans. Allow to cool completely, then cut each cake in half horizontally, making 4 layers total. If your cake is domed at the top, cut off the dome portion with a serrated knife so the tops are flat. Brush off as many crumbs as you can.

Preheat the oven to 300 degrees. Line a baking sheet with parchment paper or foil for easy cleanup.

Pop the popcorn according to the package directions and while still hot, pour into a large bowl and mix with ¾ cup of the caramel sauce. Spread the popcorn onto the prepared baking sheet and bake for 15 minutes, stirring once or twice. Let the popcorn cool completely on the baking sheet.

Combine the 2 jars of frosting with 6 tablespoons of caramel sauce. Place one cake layer on a platter or cake plate and spread a little less than a quarter of the frosting on top. Repeat with the remaining layers, frost the sides of the cake and spread the caramel popcorn on top of the cake. Drizzle the remaining 4 tablespoons of caramel on the cake. Serve immediately or refrigerate until serving.