Arrange a rack in the middle of the oven and heat the oven to 350°F. Line the bottom and sides of a 9x13-inch baking pan with 2 sheets of parchment paper, positioning them perpendicular to each other and making sure they are long enough to hang over all four sides by at least 1 inch to form a sling.

Coarsely chop 1 cup pecans. Place 6 tablespoons unsalted butter in a large microwave-safe bowl. Microwave on HIGH until just melted, about 40 seconds (alternatively, melt on the stovetop and pour into a large bowl).

Place 12 full graham cracker sheets in a large zip-top plastic bag. Seal the bag, then crush with a rolling pin or flat side of a meat mallet into finely ground crumbs (about 1 ½ cups). Transfer to the bowl of butter, add ¼ teaspoon kosher salt, and stir until evenly moistened.

Transfer the mixture to the baking pan. Using a flat-bottomed measuring cup, press it evenly into the bottom and to the corners. The mixture may be slightly crumbly.

Sprinkle 1 cup semi-sweet chocolate chips and 1 cup butterscotch chips evenly over the graham cracker layer. Sprinkle 1 cup sweetened or unsweetened shredded coconut evenly over the chocolate and butterscotch chips. Sprinkle the pecans evenly over the coconut. Pour 1 (14-ounce) can sweetened condensed milk evenly over the top to finish. The milk will naturally spread to cover the bars, so there is no need to spread it with a spoon or spatula.

Bake until golden brown, 25 to 30 minutes. Place on a wire rack and let cool completely, 1 to 2 hours. Grasping the excess parchment paper, lift the slab out of the pan and place on a cutting board. Cut into 20 bars.