Pop the kernels using your preferred popping method. Place the popped popcorn in a very large bowl and add the walnuts. Note: There should be enough room in your bowl for tossing the popcorn.

Preheat the oven to 250° F and line 2 baking sheets with parchment paper. Set aside.

Make the caramel – Melt the butter in a medium saucepan set over medium heat.  Once the butter has melted, add the corn syrup, brown sugar, apple juice, and salt. Whisk until the mixture comes together, and then increase the heat to medium-high and bring it to a boil, whisking frequently.

Once the mixture reaches a boil, allow it to continuously boil for about 7-8 minutes without stirring.  Remove the mixture from the heat and stir in the baking soda, vanilla extract, apple butter, and maple syrup.  The mixture will bubble up a bit and froth (stand back).  Whisk until all the liquid is combined and smooth. Pour the apple/caramel sauce over the popcorn and toss to coat thoroughly with a silicone spatula. You can use salad tongs as well, but I find silicone spatulas work best for me.

Spread the popcorn evenly onto your prepared baking sheets.  If it’s clumpy, that’s fine – The caramel will melt and will eventually coat all the kernels evenly.

Bake for 40-50 minutes, tossing the popcorn with tongs every 10 minutes or so to incorporate the caramel evenly.

After about 40 minutes, remove a couple of pieces of popcorn from the baking trays and allow them to come to room temperature.  If they’re not completely crispy and still mushy when you bite into them, bake for 5-8 more minutes. Continue checking this way until the popcorn has a crisp bite to it.

Remove the baking sheets to a wire rack and allow popcorn to cool completely before breaking apart for serving or packaging.