Preheat your oven to 350 degrees F. Line a 9 x 13-inch pan with parchment paper, leaving an overhang for easy removal.
Place the graham cracker crumbs into a large bowl and pour the melted butter over them. Mix together thoroughly with a whisk. Note: If you cannot find already crushed graham crackers at the grocery store, just place about 20-24 (about 160g) Graham cracker squares in a gallon-sized Ziploc bag, and crush them up with a rolling pin. You can also pulse them in a food processor to speed up the process.
Gently press the buttery graham cracker mixture into the bottom of your prepared 9 x 13 inch baking dish. Be careful not to compact the crust too firmly or it will be hard and dense instead of tender and buttery.
Spread an even layer of the following ingredients in this order: semisweet chips, butterscotch chips, chopped nuts, coconut flakes, and sweetened condensed milk. Tip: This is optional, but I like to top off the bars with a few extra morsels of semisweet and butterscotch chips.
Bake for about 25-30 minutes or just until the sides have bubbled and coconut has slightly browned.
While the dessert is still hot, sprinkle a little bit of flaky sea salt on top. This step is optional, but I recommend it to balance out the sweetness of the bars.
Once they are cooled, slice the bars into squares and enjoy!