Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the long sides to lift the bars out later. Lightly spray the parchment with nonstick spray.

In a medium bowl, mix the graham cracker crumbs, melted butter, and fine sea salt until the crumbs look like damp sand and hold together when pressed.

Pour the crumb mixture into the prepared pan. Use your hands or the bottom of a measuring cup to press it firmly and evenly into the bottom, getting into the corners and packing it well for a sturdy base.

Sprinkle the semisweet chocolate chips evenly over the crust, followed by the butterscotch chips, scattering them so every bite has a little of both.

Add the chopped nuts in an even layer over the chips.

Sprinkle the sweetened coconut flakes evenly over the nuts, covering most of the surface to help protect the chips and create a toasted golden top.

If using vanilla, stir it into the sweetened condensed milk. Slowly drizzle the condensed milk evenly over the entire pan, moving back and forth so it soaks into all the layers. Some coconut may remain exposed; it will toast in the oven.

Bake for 23–28 minutes, or until the edges are deep golden brown and the center is bubbly and lightly golden. The coconut should be nicely toasted but not burnt. Start checking around 22 minutes and tent loosely with foil if the edges brown too quickly.

Let the pan cool on a wire rack for at least 1–2 hours. For the neatest slices, chill the cooled pan in the refrigerator for an additional 30–60 minutes.

Use the parchment overhang to lift the slab out of the pan. Place on a cutting board and use a long, sharp knife to cut into small squares or rectangles, pressing straight down and wiping the knife with a warm, damp cloth between cuts. If desired, sprinkle mini chocolate chips on top while the bars are still slightly warm so they adhere. Serve at room temperature or slightly chilled.